forked from Minki/linux
d524dac927
The device tree is used by more than just PowerPC. Make the documentation
directory available to all.
v2: reorganized files while moving to create arch and driver specific
directories.
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
1448 lines
59 KiB
Plaintext
1448 lines
59 KiB
Plaintext
Booting the Linux/ppc kernel without Open Firmware
|
|
--------------------------------------------------
|
|
|
|
(c) 2005 Benjamin Herrenschmidt <benh at kernel.crashing.org>,
|
|
IBM Corp.
|
|
(c) 2005 Becky Bruce <becky.bruce at freescale.com>,
|
|
Freescale Semiconductor, FSL SOC and 32-bit additions
|
|
(c) 2006 MontaVista Software, Inc.
|
|
Flash chip node definition
|
|
|
|
Table of Contents
|
|
=================
|
|
|
|
I - Introduction
|
|
1) Entry point for arch/powerpc
|
|
2) Board support
|
|
|
|
II - The DT block format
|
|
1) Header
|
|
2) Device tree generalities
|
|
3) Device tree "structure" block
|
|
4) Device tree "strings" block
|
|
|
|
III - Required content of the device tree
|
|
1) Note about cells and address representation
|
|
2) Note about "compatible" properties
|
|
3) Note about "name" properties
|
|
4) Note about node and property names and character set
|
|
5) Required nodes and properties
|
|
a) The root node
|
|
b) The /cpus node
|
|
c) The /cpus/* nodes
|
|
d) the /memory node(s)
|
|
e) The /chosen node
|
|
f) the /soc<SOCname> node
|
|
|
|
IV - "dtc", the device tree compiler
|
|
|
|
V - Recommendations for a bootloader
|
|
|
|
VI - System-on-a-chip devices and nodes
|
|
1) Defining child nodes of an SOC
|
|
2) Representing devices without a current OF specification
|
|
a) PHY nodes
|
|
b) Interrupt controllers
|
|
c) 4xx/Axon EMAC ethernet nodes
|
|
d) Xilinx IP cores
|
|
e) USB EHCI controllers
|
|
f) MDIO on GPIOs
|
|
g) SPI busses
|
|
|
|
VII - Specifying interrupt information for devices
|
|
1) interrupts property
|
|
2) interrupt-parent property
|
|
3) OpenPIC Interrupt Controllers
|
|
4) ISA Interrupt Controllers
|
|
|
|
VIII - Specifying device power management information (sleep property)
|
|
|
|
Appendix A - Sample SOC node for MPC8540
|
|
|
|
|
|
Revision Information
|
|
====================
|
|
|
|
May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet.
|
|
|
|
May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or
|
|
clarifies the fact that a lot of things are
|
|
optional, the kernel only requires a very
|
|
small device tree, though it is encouraged
|
|
to provide an as complete one as possible.
|
|
|
|
May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM
|
|
- Misc fixes
|
|
- Define version 3 and new format version 16
|
|
for the DT block (version 16 needs kernel
|
|
patches, will be fwd separately).
|
|
String block now has a size, and full path
|
|
is replaced by unit name for more
|
|
compactness.
|
|
linux,phandle is made optional, only nodes
|
|
that are referenced by other nodes need it.
|
|
"name" property is now automatically
|
|
deduced from the unit name
|
|
|
|
June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and
|
|
OF_DT_END_NODE in structure definition.
|
|
- Change version 16 format to always align
|
|
property data to 4 bytes. Since tokens are
|
|
already aligned, that means no specific
|
|
required alignment between property size
|
|
and property data. The old style variable
|
|
alignment would make it impossible to do
|
|
"simple" insertion of properties using
|
|
memmove (thanks Milton for
|
|
noticing). Updated kernel patch as well
|
|
- Correct a few more alignment constraints
|
|
- Add a chapter about the device-tree
|
|
compiler and the textural representation of
|
|
the tree that can be "compiled" by dtc.
|
|
|
|
November 21, 2005: Rev 0.5
|
|
- Additions/generalizations for 32-bit
|
|
- Changed to reflect the new arch/powerpc
|
|
structure
|
|
- Added chapter VI
|
|
|
|
|
|
ToDo:
|
|
- Add some definitions of interrupt tree (simple/complex)
|
|
- Add some definitions for PCI host bridges
|
|
- Add some common address format examples
|
|
- Add definitions for standard properties and "compatible"
|
|
names for cells that are not already defined by the existing
|
|
OF spec.
|
|
- Compare FSL SOC use of PCI to standard and make sure no new
|
|
node definition required.
|
|
- Add more information about node definitions for SOC devices
|
|
that currently have no standard, like the FSL CPM.
|
|
|
|
|
|
I - Introduction
|
|
================
|
|
|
|
During the recent development of the Linux/ppc64 kernel, and more
|
|
specifically, the addition of new platform types outside of the old
|
|
IBM pSeries/iSeries pair, it was decided to enforce some strict rules
|
|
regarding the kernel entry and bootloader <-> kernel interfaces, in
|
|
order to avoid the degeneration that had become the ppc32 kernel entry
|
|
point and the way a new platform should be added to the kernel. The
|
|
legacy iSeries platform breaks those rules as it predates this scheme,
|
|
but no new board support will be accepted in the main tree that
|
|
doesn't follow them properly. In addition, since the advent of the
|
|
arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit
|
|
platforms and 32-bit platforms which move into arch/powerpc will be
|
|
required to use these rules as well.
|
|
|
|
The main requirement that will be defined in more detail below is
|
|
the presence of a device-tree whose format is defined after Open
|
|
Firmware specification. However, in order to make life easier
|
|
to embedded board vendors, the kernel doesn't require the device-tree
|
|
to represent every device in the system and only requires some nodes
|
|
and properties to be present. This will be described in detail in
|
|
section III, but, for example, the kernel does not require you to
|
|
create a node for every PCI device in the system. It is a requirement
|
|
to have a node for PCI host bridges in order to provide interrupt
|
|
routing informations and memory/IO ranges, among others. It is also
|
|
recommended to define nodes for on chip devices and other busses that
|
|
don't specifically fit in an existing OF specification. This creates a
|
|
great flexibility in the way the kernel can then probe those and match
|
|
drivers to device, without having to hard code all sorts of tables. It
|
|
also makes it more flexible for board vendors to do minor hardware
|
|
upgrades without significantly impacting the kernel code or cluttering
|
|
it with special cases.
|
|
|
|
|
|
1) Entry point for arch/powerpc
|
|
-------------------------------
|
|
|
|
There is one and one single entry point to the kernel, at the start
|
|
of the kernel image. That entry point supports two calling
|
|
conventions:
|
|
|
|
a) Boot from Open Firmware. If your firmware is compatible
|
|
with Open Firmware (IEEE 1275) or provides an OF compatible
|
|
client interface API (support for "interpret" callback of
|
|
forth words isn't required), you can enter the kernel with:
|
|
|
|
r5 : OF callback pointer as defined by IEEE 1275
|
|
bindings to powerpc. Only the 32-bit client interface
|
|
is currently supported
|
|
|
|
r3, r4 : address & length of an initrd if any or 0
|
|
|
|
The MMU is either on or off; the kernel will run the
|
|
trampoline located in arch/powerpc/kernel/prom_init.c to
|
|
extract the device-tree and other information from open
|
|
firmware and build a flattened device-tree as described
|
|
in b). prom_init() will then re-enter the kernel using
|
|
the second method. This trampoline code runs in the
|
|
context of the firmware, which is supposed to handle all
|
|
exceptions during that time.
|
|
|
|
b) Direct entry with a flattened device-tree block. This entry
|
|
point is called by a) after the OF trampoline and can also be
|
|
called directly by a bootloader that does not support the Open
|
|
Firmware client interface. It is also used by "kexec" to
|
|
implement "hot" booting of a new kernel from a previous
|
|
running one. This method is what I will describe in more
|
|
details in this document, as method a) is simply standard Open
|
|
Firmware, and thus should be implemented according to the
|
|
various standard documents defining it and its binding to the
|
|
PowerPC platform. The entry point definition then becomes:
|
|
|
|
r3 : physical pointer to the device-tree block
|
|
(defined in chapter II) in RAM
|
|
|
|
r4 : physical pointer to the kernel itself. This is
|
|
used by the assembly code to properly disable the MMU
|
|
in case you are entering the kernel with MMU enabled
|
|
and a non-1:1 mapping.
|
|
|
|
r5 : NULL (as to differentiate with method a)
|
|
|
|
Note about SMP entry: Either your firmware puts your other
|
|
CPUs in some sleep loop or spin loop in ROM where you can get
|
|
them out via a soft reset or some other means, in which case
|
|
you don't need to care, or you'll have to enter the kernel
|
|
with all CPUs. The way to do that with method b) will be
|
|
described in a later revision of this document.
|
|
|
|
|
|
2) Board support
|
|
----------------
|
|
|
|
64-bit kernels:
|
|
|
|
Board supports (platforms) are not exclusive config options. An
|
|
arbitrary set of board supports can be built in a single kernel
|
|
image. The kernel will "know" what set of functions to use for a
|
|
given platform based on the content of the device-tree. Thus, you
|
|
should:
|
|
|
|
a) add your platform support as a _boolean_ option in
|
|
arch/powerpc/Kconfig, following the example of PPC_PSERIES,
|
|
PPC_PMAC and PPC_MAPLE. The later is probably a good
|
|
example of a board support to start from.
|
|
|
|
b) create your main platform file as
|
|
"arch/powerpc/platforms/myplatform/myboard_setup.c" and add it
|
|
to the Makefile under the condition of your CONFIG_
|
|
option. This file will define a structure of type "ppc_md"
|
|
containing the various callbacks that the generic code will
|
|
use to get to your platform specific code
|
|
|
|
c) Add a reference to your "ppc_md" structure in the
|
|
"machines" table in arch/powerpc/kernel/setup_64.c if you are
|
|
a 64-bit platform.
|
|
|
|
d) request and get assigned a platform number (see PLATFORM_*
|
|
constants in arch/powerpc/include/asm/processor.h
|
|
|
|
32-bit embedded kernels:
|
|
|
|
Currently, board support is essentially an exclusive config option.
|
|
The kernel is configured for a single platform. Part of the reason
|
|
for this is to keep kernels on embedded systems small and efficient;
|
|
part of this is due to the fact the code is already that way. In the
|
|
future, a kernel may support multiple platforms, but only if the
|
|
platforms feature the same core architecture. A single kernel build
|
|
cannot support both configurations with Book E and configurations
|
|
with classic Powerpc architectures.
|
|
|
|
32-bit embedded platforms that are moved into arch/powerpc using a
|
|
flattened device tree should adopt the merged tree practice of
|
|
setting ppc_md up dynamically, even though the kernel is currently
|
|
built with support for only a single platform at a time. This allows
|
|
unification of the setup code, and will make it easier to go to a
|
|
multiple-platform-support model in the future.
|
|
|
|
NOTE: I believe the above will be true once Ben's done with the merge
|
|
of the boot sequences.... someone speak up if this is wrong!
|
|
|
|
To add a 32-bit embedded platform support, follow the instructions
|
|
for 64-bit platforms above, with the exception that the Kconfig
|
|
option should be set up such that the kernel builds exclusively for
|
|
the platform selected. The processor type for the platform should
|
|
enable another config option to select the specific board
|
|
supported.
|
|
|
|
NOTE: If Ben doesn't merge the setup files, may need to change this to
|
|
point to setup_32.c
|
|
|
|
|
|
I will describe later the boot process and various callbacks that
|
|
your platform should implement.
|
|
|
|
|
|
II - The DT block format
|
|
========================
|
|
|
|
|
|
This chapter defines the actual format of the flattened device-tree
|
|
passed to the kernel. The actual content of it and kernel requirements
|
|
are described later. You can find example of code manipulating that
|
|
format in various places, including arch/powerpc/kernel/prom_init.c
|
|
which will generate a flattened device-tree from the Open Firmware
|
|
representation, or the fs2dt utility which is part of the kexec tools
|
|
which will generate one from a filesystem representation. It is
|
|
expected that a bootloader like uboot provides a bit more support,
|
|
that will be discussed later as well.
|
|
|
|
Note: The block has to be in main memory. It has to be accessible in
|
|
both real mode and virtual mode with no mapping other than main
|
|
memory. If you are writing a simple flash bootloader, it should copy
|
|
the block to RAM before passing it to the kernel.
|
|
|
|
|
|
1) Header
|
|
---------
|
|
|
|
The kernel is entered with r3 pointing to an area of memory that is
|
|
roughly described in arch/powerpc/include/asm/prom.h by the structure
|
|
boot_param_header:
|
|
|
|
struct boot_param_header {
|
|
u32 magic; /* magic word OF_DT_HEADER */
|
|
u32 totalsize; /* total size of DT block */
|
|
u32 off_dt_struct; /* offset to structure */
|
|
u32 off_dt_strings; /* offset to strings */
|
|
u32 off_mem_rsvmap; /* offset to memory reserve map
|
|
*/
|
|
u32 version; /* format version */
|
|
u32 last_comp_version; /* last compatible version */
|
|
|
|
/* version 2 fields below */
|
|
u32 boot_cpuid_phys; /* Which physical CPU id we're
|
|
booting on */
|
|
/* version 3 fields below */
|
|
u32 size_dt_strings; /* size of the strings block */
|
|
|
|
/* version 17 fields below */
|
|
u32 size_dt_struct; /* size of the DT structure block */
|
|
};
|
|
|
|
Along with the constants:
|
|
|
|
/* Definitions used by the flattened device tree */
|
|
#define OF_DT_HEADER 0xd00dfeed /* 4: version,
|
|
4: total size */
|
|
#define OF_DT_BEGIN_NODE 0x1 /* Start node: full name
|
|
*/
|
|
#define OF_DT_END_NODE 0x2 /* End node */
|
|
#define OF_DT_PROP 0x3 /* Property: name off,
|
|
size, content */
|
|
#define OF_DT_END 0x9
|
|
|
|
All values in this header are in big endian format, the various
|
|
fields in this header are defined more precisely below. All
|
|
"offset" values are in bytes from the start of the header; that is
|
|
from the value of r3.
|
|
|
|
- magic
|
|
|
|
This is a magic value that "marks" the beginning of the
|
|
device-tree block header. It contains the value 0xd00dfeed and is
|
|
defined by the constant OF_DT_HEADER
|
|
|
|
- totalsize
|
|
|
|
This is the total size of the DT block including the header. The
|
|
"DT" block should enclose all data structures defined in this
|
|
chapter (who are pointed to by offsets in this header). That is,
|
|
the device-tree structure, strings, and the memory reserve map.
|
|
|
|
- off_dt_struct
|
|
|
|
This is an offset from the beginning of the header to the start
|
|
of the "structure" part the device tree. (see 2) device tree)
|
|
|
|
- off_dt_strings
|
|
|
|
This is an offset from the beginning of the header to the start
|
|
of the "strings" part of the device-tree
|
|
|
|
- off_mem_rsvmap
|
|
|
|
This is an offset from the beginning of the header to the start
|
|
of the reserved memory map. This map is a list of pairs of 64-
|
|
bit integers. Each pair is a physical address and a size. The
|
|
list is terminated by an entry of size 0. This map provides the
|
|
kernel with a list of physical memory areas that are "reserved"
|
|
and thus not to be used for memory allocations, especially during
|
|
early initialization. The kernel needs to allocate memory during
|
|
boot for things like un-flattening the device-tree, allocating an
|
|
MMU hash table, etc... Those allocations must be done in such a
|
|
way to avoid overriding critical things like, on Open Firmware
|
|
capable machines, the RTAS instance, or on some pSeries, the TCE
|
|
tables used for the iommu. Typically, the reserve map should
|
|
contain _at least_ this DT block itself (header,total_size). If
|
|
you are passing an initrd to the kernel, you should reserve it as
|
|
well. You do not need to reserve the kernel image itself. The map
|
|
should be 64-bit aligned.
|
|
|
|
- version
|
|
|
|
This is the version of this structure. Version 1 stops
|
|
here. Version 2 adds an additional field boot_cpuid_phys.
|
|
Version 3 adds the size of the strings block, allowing the kernel
|
|
to reallocate it easily at boot and free up the unused flattened
|
|
structure after expansion. Version 16 introduces a new more
|
|
"compact" format for the tree itself that is however not backward
|
|
compatible. Version 17 adds an additional field, size_dt_struct,
|
|
allowing it to be reallocated or moved more easily (this is
|
|
particularly useful for bootloaders which need to make
|
|
adjustments to a device tree based on probed information). You
|
|
should always generate a structure of the highest version defined
|
|
at the time of your implementation. Currently that is version 17,
|
|
unless you explicitly aim at being backward compatible.
|
|
|
|
- last_comp_version
|
|
|
|
Last compatible version. This indicates down to what version of
|
|
the DT block you are backward compatible. For example, version 2
|
|
is backward compatible with version 1 (that is, a kernel build
|
|
for version 1 will be able to boot with a version 2 format). You
|
|
should put a 1 in this field if you generate a device tree of
|
|
version 1 to 3, or 16 if you generate a tree of version 16 or 17
|
|
using the new unit name format.
|
|
|
|
- boot_cpuid_phys
|
|
|
|
This field only exist on version 2 headers. It indicate which
|
|
physical CPU ID is calling the kernel entry point. This is used,
|
|
among others, by kexec. If you are on an SMP system, this value
|
|
should match the content of the "reg" property of the CPU node in
|
|
the device-tree corresponding to the CPU calling the kernel entry
|
|
point (see further chapters for more informations on the required
|
|
device-tree contents)
|
|
|
|
- size_dt_strings
|
|
|
|
This field only exists on version 3 and later headers. It
|
|
gives the size of the "strings" section of the device tree (which
|
|
starts at the offset given by off_dt_strings).
|
|
|
|
- size_dt_struct
|
|
|
|
This field only exists on version 17 and later headers. It gives
|
|
the size of the "structure" section of the device tree (which
|
|
starts at the offset given by off_dt_struct).
|
|
|
|
So the typical layout of a DT block (though the various parts don't
|
|
need to be in that order) looks like this (addresses go from top to
|
|
bottom):
|
|
|
|
|
|
------------------------------
|
|
r3 -> | struct boot_param_header |
|
|
------------------------------
|
|
| (alignment gap) (*) |
|
|
------------------------------
|
|
| memory reserve map |
|
|
------------------------------
|
|
| (alignment gap) |
|
|
------------------------------
|
|
| |
|
|
| device-tree structure |
|
|
| |
|
|
------------------------------
|
|
| (alignment gap) |
|
|
------------------------------
|
|
| |
|
|
| device-tree strings |
|
|
| |
|
|
-----> ------------------------------
|
|
|
|
|
|
|
|
--- (r3 + totalsize)
|
|
|
|
(*) The alignment gaps are not necessarily present; their presence
|
|
and size are dependent on the various alignment requirements of
|
|
the individual data blocks.
|
|
|
|
|
|
2) Device tree generalities
|
|
---------------------------
|
|
|
|
This device-tree itself is separated in two different blocks, a
|
|
structure block and a strings block. Both need to be aligned to a 4
|
|
byte boundary.
|
|
|
|
First, let's quickly describe the device-tree concept before detailing
|
|
the storage format. This chapter does _not_ describe the detail of the
|
|
required types of nodes & properties for the kernel, this is done
|
|
later in chapter III.
|
|
|
|
The device-tree layout is strongly inherited from the definition of
|
|
the Open Firmware IEEE 1275 device-tree. It's basically a tree of
|
|
nodes, each node having two or more named properties. A property can
|
|
have a value or not.
|
|
|
|
It is a tree, so each node has one and only one parent except for the
|
|
root node who has no parent.
|
|
|
|
A node has 2 names. The actual node name is generally contained in a
|
|
property of type "name" in the node property list whose value is a
|
|
zero terminated string and is mandatory for version 1 to 3 of the
|
|
format definition (as it is in Open Firmware). Version 16 makes it
|
|
optional as it can generate it from the unit name defined below.
|
|
|
|
There is also a "unit name" that is used to differentiate nodes with
|
|
the same name at the same level, it is usually made of the node
|
|
names, the "@" sign, and a "unit address", which definition is
|
|
specific to the bus type the node sits on.
|
|
|
|
The unit name doesn't exist as a property per-se but is included in
|
|
the device-tree structure. It is typically used to represent "path" in
|
|
the device-tree. More details about the actual format of these will be
|
|
below.
|
|
|
|
The kernel powerpc generic code does not make any formal use of the
|
|
unit address (though some board support code may do) so the only real
|
|
requirement here for the unit address is to ensure uniqueness of
|
|
the node unit name at a given level of the tree. Nodes with no notion
|
|
of address and no possible sibling of the same name (like /memory or
|
|
/cpus) may omit the unit address in the context of this specification,
|
|
or use the "@0" default unit address. The unit name is used to define
|
|
a node "full path", which is the concatenation of all parent node
|
|
unit names separated with "/".
|
|
|
|
The root node doesn't have a defined name, and isn't required to have
|
|
a name property either if you are using version 3 or earlier of the
|
|
format. It also has no unit address (no @ symbol followed by a unit
|
|
address). The root node unit name is thus an empty string. The full
|
|
path to the root node is "/".
|
|
|
|
Every node which actually represents an actual device (that is, a node
|
|
which isn't only a virtual "container" for more nodes, like "/cpus"
|
|
is) is also required to have a "device_type" property indicating the
|
|
type of node .
|
|
|
|
Finally, every node that can be referenced from a property in another
|
|
node is required to have a "linux,phandle" property. Real open
|
|
firmware implementations provide a unique "phandle" value for every
|
|
node that the "prom_init()" trampoline code turns into
|
|
"linux,phandle" properties. However, this is made optional if the
|
|
flattened device tree is used directly. An example of a node
|
|
referencing another node via "phandle" is when laying out the
|
|
interrupt tree which will be described in a further version of this
|
|
document.
|
|
|
|
This "linux, phandle" property is a 32-bit value that uniquely
|
|
identifies a node. You are free to use whatever values or system of
|
|
values, internal pointers, or whatever to generate these, the only
|
|
requirement is that every node for which you provide that property has
|
|
a unique value for it.
|
|
|
|
Here is an example of a simple device-tree. In this example, an "o"
|
|
designates a node followed by the node unit name. Properties are
|
|
presented with their name followed by their content. "content"
|
|
represents an ASCII string (zero terminated) value, while <content>
|
|
represents a 32-bit hexadecimal value. The various nodes in this
|
|
example will be discussed in a later chapter. At this point, it is
|
|
only meant to give you a idea of what a device-tree looks like. I have
|
|
purposefully kept the "name" and "linux,phandle" properties which
|
|
aren't necessary in order to give you a better idea of what the tree
|
|
looks like in practice.
|
|
|
|
/ o device-tree
|
|
|- name = "device-tree"
|
|
|- model = "MyBoardName"
|
|
|- compatible = "MyBoardFamilyName"
|
|
|- #address-cells = <2>
|
|
|- #size-cells = <2>
|
|
|- linux,phandle = <0>
|
|
|
|
|
o cpus
|
|
| | - name = "cpus"
|
|
| | - linux,phandle = <1>
|
|
| | - #address-cells = <1>
|
|
| | - #size-cells = <0>
|
|
| |
|
|
| o PowerPC,970@0
|
|
| |- name = "PowerPC,970"
|
|
| |- device_type = "cpu"
|
|
| |- reg = <0>
|
|
| |- clock-frequency = <5f5e1000>
|
|
| |- 64-bit
|
|
| |- linux,phandle = <2>
|
|
|
|
|
o memory@0
|
|
| |- name = "memory"
|
|
| |- device_type = "memory"
|
|
| |- reg = <00000000 00000000 00000000 20000000>
|
|
| |- linux,phandle = <3>
|
|
|
|
|
o chosen
|
|
|- name = "chosen"
|
|
|- bootargs = "root=/dev/sda2"
|
|
|- linux,phandle = <4>
|
|
|
|
This tree is almost a minimal tree. It pretty much contains the
|
|
minimal set of required nodes and properties to boot a linux kernel;
|
|
that is, some basic model informations at the root, the CPUs, and the
|
|
physical memory layout. It also includes misc information passed
|
|
through /chosen, like in this example, the platform type (mandatory)
|
|
and the kernel command line arguments (optional).
|
|
|
|
The /cpus/PowerPC,970@0/64-bit property is an example of a
|
|
property without a value. All other properties have a value. The
|
|
significance of the #address-cells and #size-cells properties will be
|
|
explained in chapter IV which defines precisely the required nodes and
|
|
properties and their content.
|
|
|
|
|
|
3) Device tree "structure" block
|
|
|
|
The structure of the device tree is a linearized tree structure. The
|
|
"OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE"
|
|
ends that node definition. Child nodes are simply defined before
|
|
"OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32
|
|
bit value. The tree has to be "finished" with a OF_DT_END token
|
|
|
|
Here's the basic structure of a single node:
|
|
|
|
* token OF_DT_BEGIN_NODE (that is 0x00000001)
|
|
* for version 1 to 3, this is the node full path as a zero
|
|
terminated string, starting with "/". For version 16 and later,
|
|
this is the node unit name only (or an empty string for the
|
|
root node)
|
|
* [align gap to next 4 bytes boundary]
|
|
* for each property:
|
|
* token OF_DT_PROP (that is 0x00000003)
|
|
* 32-bit value of property value size in bytes (or 0 if no
|
|
value)
|
|
* 32-bit value of offset in string block of property name
|
|
* property value data if any
|
|
* [align gap to next 4 bytes boundary]
|
|
* [child nodes if any]
|
|
* token OF_DT_END_NODE (that is 0x00000002)
|
|
|
|
So the node content can be summarized as a start token, a full path,
|
|
a list of properties, a list of child nodes, and an end token. Every
|
|
child node is a full node structure itself as defined above.
|
|
|
|
NOTE: The above definition requires that all property definitions for
|
|
a particular node MUST precede any subnode definitions for that node.
|
|
Although the structure would not be ambiguous if properties and
|
|
subnodes were intermingled, the kernel parser requires that the
|
|
properties come first (up until at least 2.6.22). Any tools
|
|
manipulating a flattened tree must take care to preserve this
|
|
constraint.
|
|
|
|
4) Device tree "strings" block
|
|
|
|
In order to save space, property names, which are generally redundant,
|
|
are stored separately in the "strings" block. This block is simply the
|
|
whole bunch of zero terminated strings for all property names
|
|
concatenated together. The device-tree property definitions in the
|
|
structure block will contain offset values from the beginning of the
|
|
strings block.
|
|
|
|
|
|
III - Required content of the device tree
|
|
=========================================
|
|
|
|
WARNING: All "linux,*" properties defined in this document apply only
|
|
to a flattened device-tree. If your platform uses a real
|
|
implementation of Open Firmware or an implementation compatible with
|
|
the Open Firmware client interface, those properties will be created
|
|
by the trampoline code in the kernel's prom_init() file. For example,
|
|
that's where you'll have to add code to detect your board model and
|
|
set the platform number. However, when using the flattened device-tree
|
|
entry point, there is no prom_init() pass, and thus you have to
|
|
provide those properties yourself.
|
|
|
|
|
|
1) Note about cells and address representation
|
|
----------------------------------------------
|
|
|
|
The general rule is documented in the various Open Firmware
|
|
documentations. If you choose to describe a bus with the device-tree
|
|
and there exist an OF bus binding, then you should follow the
|
|
specification. However, the kernel does not require every single
|
|
device or bus to be described by the device tree.
|
|
|
|
In general, the format of an address for a device is defined by the
|
|
parent bus type, based on the #address-cells and #size-cells
|
|
properties. Note that the parent's parent definitions of #address-cells
|
|
and #size-cells are not inherited so every node with children must specify
|
|
them. The kernel requires the root node to have those properties defining
|
|
addresses format for devices directly mapped on the processor bus.
|
|
|
|
Those 2 properties define 'cells' for representing an address and a
|
|
size. A "cell" is a 32-bit number. For example, if both contain 2
|
|
like the example tree given above, then an address and a size are both
|
|
composed of 2 cells, and each is a 64-bit number (cells are
|
|
concatenated and expected to be in big endian format). Another example
|
|
is the way Apple firmware defines them, with 2 cells for an address
|
|
and one cell for a size. Most 32-bit implementations should define
|
|
#address-cells and #size-cells to 1, which represents a 32-bit value.
|
|
Some 32-bit processors allow for physical addresses greater than 32
|
|
bits; these processors should define #address-cells as 2.
|
|
|
|
"reg" properties are always a tuple of the type "address size" where
|
|
the number of cells of address and size is specified by the bus
|
|
#address-cells and #size-cells. When a bus supports various address
|
|
spaces and other flags relative to a given address allocation (like
|
|
prefetchable, etc...) those flags are usually added to the top level
|
|
bits of the physical address. For example, a PCI physical address is
|
|
made of 3 cells, the bottom two containing the actual address itself
|
|
while the top cell contains address space indication, flags, and pci
|
|
bus & device numbers.
|
|
|
|
For busses that support dynamic allocation, it's the accepted practice
|
|
to then not provide the address in "reg" (keep it 0) though while
|
|
providing a flag indicating the address is dynamically allocated, and
|
|
then, to provide a separate "assigned-addresses" property that
|
|
contains the fully allocated addresses. See the PCI OF bindings for
|
|
details.
|
|
|
|
In general, a simple bus with no address space bits and no dynamic
|
|
allocation is preferred if it reflects your hardware, as the existing
|
|
kernel address parsing functions will work out of the box. If you
|
|
define a bus type with a more complex address format, including things
|
|
like address space bits, you'll have to add a bus translator to the
|
|
prom_parse.c file of the recent kernels for your bus type.
|
|
|
|
The "reg" property only defines addresses and sizes (if #size-cells is
|
|
non-0) within a given bus. In order to translate addresses upward
|
|
(that is into parent bus addresses, and possibly into CPU physical
|
|
addresses), all busses must contain a "ranges" property. If the
|
|
"ranges" property is missing at a given level, it's assumed that
|
|
translation isn't possible, i.e., the registers are not visible on the
|
|
parent bus. The format of the "ranges" property for a bus is a list
|
|
of:
|
|
|
|
bus address, parent bus address, size
|
|
|
|
"bus address" is in the format of the bus this bus node is defining,
|
|
that is, for a PCI bridge, it would be a PCI address. Thus, (bus
|
|
address, size) defines a range of addresses for child devices. "parent
|
|
bus address" is in the format of the parent bus of this bus. For
|
|
example, for a PCI host controller, that would be a CPU address. For a
|
|
PCI<->ISA bridge, that would be a PCI address. It defines the base
|
|
address in the parent bus where the beginning of that range is mapped.
|
|
|
|
For a new 64-bit powerpc board, I recommend either the 2/2 format or
|
|
Apple's 2/1 format which is slightly more compact since sizes usually
|
|
fit in a single 32-bit word. New 32-bit powerpc boards should use a
|
|
1/1 format, unless the processor supports physical addresses greater
|
|
than 32-bits, in which case a 2/1 format is recommended.
|
|
|
|
Alternatively, the "ranges" property may be empty, indicating that the
|
|
registers are visible on the parent bus using an identity mapping
|
|
translation. In other words, the parent bus address space is the same
|
|
as the child bus address space.
|
|
|
|
2) Note about "compatible" properties
|
|
-------------------------------------
|
|
|
|
These properties are optional, but recommended in devices and the root
|
|
node. The format of a "compatible" property is a list of concatenated
|
|
zero terminated strings. They allow a device to express its
|
|
compatibility with a family of similar devices, in some cases,
|
|
allowing a single driver to match against several devices regardless
|
|
of their actual names.
|
|
|
|
3) Note about "name" properties
|
|
-------------------------------
|
|
|
|
While earlier users of Open Firmware like OldWorld macintoshes tended
|
|
to use the actual device name for the "name" property, it's nowadays
|
|
considered a good practice to use a name that is closer to the device
|
|
class (often equal to device_type). For example, nowadays, ethernet
|
|
controllers are named "ethernet", an additional "model" property
|
|
defining precisely the chip type/model, and "compatible" property
|
|
defining the family in case a single driver can driver more than one
|
|
of these chips. However, the kernel doesn't generally put any
|
|
restriction on the "name" property; it is simply considered good
|
|
practice to follow the standard and its evolutions as closely as
|
|
possible.
|
|
|
|
Note also that the new format version 16 makes the "name" property
|
|
optional. If it's absent for a node, then the node's unit name is then
|
|
used to reconstruct the name. That is, the part of the unit name
|
|
before the "@" sign is used (or the entire unit name if no "@" sign
|
|
is present).
|
|
|
|
4) Note about node and property names and character set
|
|
-------------------------------------------------------
|
|
|
|
While open firmware provides more flexible usage of 8859-1, this
|
|
specification enforces more strict rules. Nodes and properties should
|
|
be comprised only of ASCII characters 'a' to 'z', '0' to
|
|
'9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally
|
|
allow uppercase characters 'A' to 'Z' (property names should be
|
|
lowercase. The fact that vendors like Apple don't respect this rule is
|
|
irrelevant here). Additionally, node and property names should always
|
|
begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node
|
|
names).
|
|
|
|
The maximum number of characters for both nodes and property names
|
|
is 31. In the case of node names, this is only the leftmost part of
|
|
a unit name (the pure "name" property), it doesn't include the unit
|
|
address which can extend beyond that limit.
|
|
|
|
|
|
5) Required nodes and properties
|
|
--------------------------------
|
|
These are all that are currently required. However, it is strongly
|
|
recommended that you expose PCI host bridges as documented in the
|
|
PCI binding to open firmware, and your interrupt tree as documented
|
|
in OF interrupt tree specification.
|
|
|
|
a) The root node
|
|
|
|
The root node requires some properties to be present:
|
|
|
|
- model : this is your board name/model
|
|
- #address-cells : address representation for "root" devices
|
|
- #size-cells: the size representation for "root" devices
|
|
- device_type : This property shouldn't be necessary. However, if
|
|
you decide to create a device_type for your root node, make sure it
|
|
is _not_ "chrp" unless your platform is a pSeries or PAPR compliant
|
|
one for 64-bit, or a CHRP-type machine for 32-bit as this will
|
|
matched by the kernel this way.
|
|
|
|
Additionally, some recommended properties are:
|
|
|
|
- compatible : the board "family" generally finds its way here,
|
|
for example, if you have 2 board models with a similar layout,
|
|
that typically get driven by the same platform code in the
|
|
kernel, you would use a different "model" property but put a
|
|
value in "compatible". The kernel doesn't directly use that
|
|
value but it is generally useful.
|
|
|
|
The root node is also generally where you add additional properties
|
|
specific to your board like the serial number if any, that sort of
|
|
thing. It is recommended that if you add any "custom" property whose
|
|
name may clash with standard defined ones, you prefix them with your
|
|
vendor name and a comma.
|
|
|
|
b) The /cpus node
|
|
|
|
This node is the parent of all individual CPU nodes. It doesn't
|
|
have any specific requirements, though it's generally good practice
|
|
to have at least:
|
|
|
|
#address-cells = <00000001>
|
|
#size-cells = <00000000>
|
|
|
|
This defines that the "address" for a CPU is a single cell, and has
|
|
no meaningful size. This is not necessary but the kernel will assume
|
|
that format when reading the "reg" properties of a CPU node, see
|
|
below
|
|
|
|
c) The /cpus/* nodes
|
|
|
|
So under /cpus, you are supposed to create a node for every CPU on
|
|
the machine. There is no specific restriction on the name of the
|
|
CPU, though It's common practice to call it PowerPC,<name>. For
|
|
example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX.
|
|
|
|
Required properties:
|
|
|
|
- device_type : has to be "cpu"
|
|
- reg : This is the physical CPU number, it's a single 32-bit cell
|
|
and is also used as-is as the unit number for constructing the
|
|
unit name in the full path. For example, with 2 CPUs, you would
|
|
have the full path:
|
|
/cpus/PowerPC,970FX@0
|
|
/cpus/PowerPC,970FX@1
|
|
(unit addresses do not require leading zeroes)
|
|
- d-cache-block-size : one cell, L1 data cache block size in bytes (*)
|
|
- i-cache-block-size : one cell, L1 instruction cache block size in
|
|
bytes
|
|
- d-cache-size : one cell, size of L1 data cache in bytes
|
|
- i-cache-size : one cell, size of L1 instruction cache in bytes
|
|
|
|
(*) The cache "block" size is the size on which the cache management
|
|
instructions operate. Historically, this document used the cache
|
|
"line" size here which is incorrect. The kernel will prefer the cache
|
|
block size and will fallback to cache line size for backward
|
|
compatibility.
|
|
|
|
Recommended properties:
|
|
|
|
- timebase-frequency : a cell indicating the frequency of the
|
|
timebase in Hz. This is not directly used by the generic code,
|
|
but you are welcome to copy/paste the pSeries code for setting
|
|
the kernel timebase/decrementer calibration based on this
|
|
value.
|
|
- clock-frequency : a cell indicating the CPU core clock frequency
|
|
in Hz. A new property will be defined for 64-bit values, but if
|
|
your frequency is < 4Ghz, one cell is enough. Here as well as
|
|
for the above, the common code doesn't use that property, but
|
|
you are welcome to re-use the pSeries or Maple one. A future
|
|
kernel version might provide a common function for this.
|
|
- d-cache-line-size : one cell, L1 data cache line size in bytes
|
|
if different from the block size
|
|
- i-cache-line-size : one cell, L1 instruction cache line size in
|
|
bytes if different from the block size
|
|
|
|
You are welcome to add any property you find relevant to your board,
|
|
like some information about the mechanism used to soft-reset the
|
|
CPUs. For example, Apple puts the GPIO number for CPU soft reset
|
|
lines in there as a "soft-reset" property since they start secondary
|
|
CPUs by soft-resetting them.
|
|
|
|
|
|
d) the /memory node(s)
|
|
|
|
To define the physical memory layout of your board, you should
|
|
create one or more memory node(s). You can either create a single
|
|
node with all memory ranges in its reg property, or you can create
|
|
several nodes, as you wish. The unit address (@ part) used for the
|
|
full path is the address of the first range of memory defined by a
|
|
given node. If you use a single memory node, this will typically be
|
|
@0.
|
|
|
|
Required properties:
|
|
|
|
- device_type : has to be "memory"
|
|
- reg : This property contains all the physical memory ranges of
|
|
your board. It's a list of addresses/sizes concatenated
|
|
together, with the number of cells of each defined by the
|
|
#address-cells and #size-cells of the root node. For example,
|
|
with both of these properties being 2 like in the example given
|
|
earlier, a 970 based machine with 6Gb of RAM could typically
|
|
have a "reg" property here that looks like:
|
|
|
|
00000000 00000000 00000000 80000000
|
|
00000001 00000000 00000001 00000000
|
|
|
|
That is a range starting at 0 of 0x80000000 bytes and a range
|
|
starting at 0x100000000 and of 0x100000000 bytes. You can see
|
|
that there is no memory covering the IO hole between 2Gb and
|
|
4Gb. Some vendors prefer splitting those ranges into smaller
|
|
segments, but the kernel doesn't care.
|
|
|
|
e) The /chosen node
|
|
|
|
This node is a bit "special". Normally, that's where open firmware
|
|
puts some variable environment information, like the arguments, or
|
|
the default input/output devices.
|
|
|
|
This specification makes a few of these mandatory, but also defines
|
|
some linux-specific properties that would be normally constructed by
|
|
the prom_init() trampoline when booting with an OF client interface,
|
|
but that you have to provide yourself when using the flattened format.
|
|
|
|
Recommended properties:
|
|
|
|
- bootargs : This zero-terminated string is passed as the kernel
|
|
command line
|
|
- linux,stdout-path : This is the full path to your standard
|
|
console device if any. Typically, if you have serial devices on
|
|
your board, you may want to put the full path to the one set as
|
|
the default console in the firmware here, for the kernel to pick
|
|
it up as its own default console. If you look at the function
|
|
set_preferred_console() in arch/ppc64/kernel/setup.c, you'll see
|
|
that the kernel tries to find out the default console and has
|
|
knowledge of various types like 8250 serial ports. You may want
|
|
to extend this function to add your own.
|
|
|
|
Note that u-boot creates and fills in the chosen node for platforms
|
|
that use it.
|
|
|
|
(Note: a practice that is now obsolete was to include a property
|
|
under /chosen called interrupt-controller which had a phandle value
|
|
that pointed to the main interrupt controller)
|
|
|
|
f) the /soc<SOCname> node
|
|
|
|
This node is used to represent a system-on-a-chip (SOC) and must be
|
|
present if the processor is a SOC. The top-level soc node contains
|
|
information that is global to all devices on the SOC. The node name
|
|
should contain a unit address for the SOC, which is the base address
|
|
of the memory-mapped register set for the SOC. The name of an soc
|
|
node should start with "soc", and the remainder of the name should
|
|
represent the part number for the soc. For example, the MPC8540's
|
|
soc node would be called "soc8540".
|
|
|
|
Required properties:
|
|
|
|
- device_type : Should be "soc"
|
|
- ranges : Should be defined as specified in 1) to describe the
|
|
translation of SOC addresses for memory mapped SOC registers.
|
|
- bus-frequency: Contains the bus frequency for the SOC node.
|
|
Typically, the value of this field is filled in by the boot
|
|
loader.
|
|
|
|
|
|
Recommended properties:
|
|
|
|
- reg : This property defines the address and size of the
|
|
memory-mapped registers that are used for the SOC node itself.
|
|
It does not include the child device registers - these will be
|
|
defined inside each child node. The address specified in the
|
|
"reg" property should match the unit address of the SOC node.
|
|
- #address-cells : Address representation for "soc" devices. The
|
|
format of this field may vary depending on whether or not the
|
|
device registers are memory mapped. For memory mapped
|
|
registers, this field represents the number of cells needed to
|
|
represent the address of the registers. For SOCs that do not
|
|
use MMIO, a special address format should be defined that
|
|
contains enough cells to represent the required information.
|
|
See 1) above for more details on defining #address-cells.
|
|
- #size-cells : Size representation for "soc" devices
|
|
- #interrupt-cells : Defines the width of cells used to represent
|
|
interrupts. Typically this value is <2>, which includes a
|
|
32-bit number that represents the interrupt number, and a
|
|
32-bit number that represents the interrupt sense and level.
|
|
This field is only needed if the SOC contains an interrupt
|
|
controller.
|
|
|
|
The SOC node may contain child nodes for each SOC device that the
|
|
platform uses. Nodes should not be created for devices which exist
|
|
on the SOC but are not used by a particular platform. See chapter VI
|
|
for more information on how to specify devices that are part of a SOC.
|
|
|
|
Example SOC node for the MPC8540:
|
|
|
|
soc8540@e0000000 {
|
|
#address-cells = <1>;
|
|
#size-cells = <1>;
|
|
#interrupt-cells = <2>;
|
|
device_type = "soc";
|
|
ranges = <00000000 e0000000 00100000>
|
|
reg = <e0000000 00003000>;
|
|
bus-frequency = <0>;
|
|
}
|
|
|
|
|
|
|
|
IV - "dtc", the device tree compiler
|
|
====================================
|
|
|
|
|
|
dtc source code can be found at
|
|
<http://git.jdl.com/gitweb/?p=dtc.git>
|
|
|
|
WARNING: This version is still in early development stage; the
|
|
resulting device-tree "blobs" have not yet been validated with the
|
|
kernel. The current generated block lacks a useful reserve map (it will
|
|
be fixed to generate an empty one, it's up to the bootloader to fill
|
|
it up) among others. The error handling needs work, bugs are lurking,
|
|
etc...
|
|
|
|
dtc basically takes a device-tree in a given format and outputs a
|
|
device-tree in another format. The currently supported formats are:
|
|
|
|
Input formats:
|
|
-------------
|
|
|
|
- "dtb": "blob" format, that is a flattened device-tree block
|
|
with
|
|
header all in a binary blob.
|
|
- "dts": "source" format. This is a text file containing a
|
|
"source" for a device-tree. The format is defined later in this
|
|
chapter.
|
|
- "fs" format. This is a representation equivalent to the
|
|
output of /proc/device-tree, that is nodes are directories and
|
|
properties are files
|
|
|
|
Output formats:
|
|
---------------
|
|
|
|
- "dtb": "blob" format
|
|
- "dts": "source" format
|
|
- "asm": assembly language file. This is a file that can be
|
|
sourced by gas to generate a device-tree "blob". That file can
|
|
then simply be added to your Makefile. Additionally, the
|
|
assembly file exports some symbols that can be used.
|
|
|
|
|
|
The syntax of the dtc tool is
|
|
|
|
dtc [-I <input-format>] [-O <output-format>]
|
|
[-o output-filename] [-V output_version] input_filename
|
|
|
|
|
|
The "output_version" defines what version of the "blob" format will be
|
|
generated. Supported versions are 1,2,3 and 16. The default is
|
|
currently version 3 but that may change in the future to version 16.
|
|
|
|
Additionally, dtc performs various sanity checks on the tree, like the
|
|
uniqueness of linux, phandle properties, validity of strings, etc...
|
|
|
|
The format of the .dts "source" file is "C" like, supports C and C++
|
|
style comments.
|
|
|
|
/ {
|
|
}
|
|
|
|
The above is the "device-tree" definition. It's the only statement
|
|
supported currently at the toplevel.
|
|
|
|
/ {
|
|
property1 = "string_value"; /* define a property containing a 0
|
|
* terminated string
|
|
*/
|
|
|
|
property2 = <1234abcd>; /* define a property containing a
|
|
* numerical 32-bit value (hexadecimal)
|
|
*/
|
|
|
|
property3 = <12345678 12345678 deadbeef>;
|
|
/* define a property containing 3
|
|
* numerical 32-bit values (cells) in
|
|
* hexadecimal
|
|
*/
|
|
property4 = [0a 0b 0c 0d de ea ad be ef];
|
|
/* define a property whose content is
|
|
* an arbitrary array of bytes
|
|
*/
|
|
|
|
childnode@address { /* define a child node named "childnode"
|
|
* whose unit name is "childnode at
|
|
* address"
|
|
*/
|
|
|
|
childprop = "hello\n"; /* define a property "childprop" of
|
|
* childnode (in this case, a string)
|
|
*/
|
|
};
|
|
};
|
|
|
|
Nodes can contain other nodes etc... thus defining the hierarchical
|
|
structure of the tree.
|
|
|
|
Strings support common escape sequences from C: "\n", "\t", "\r",
|
|
"\(octal value)", "\x(hex value)".
|
|
|
|
It is also suggested that you pipe your source file through cpp (gcc
|
|
preprocessor) so you can use #include's, #define for constants, etc...
|
|
|
|
Finally, various options are planned but not yet implemented, like
|
|
automatic generation of phandles, labels (exported to the asm file so
|
|
you can point to a property content and change it easily from whatever
|
|
you link the device-tree with), label or path instead of numeric value
|
|
in some cells to "point" to a node (replaced by a phandle at compile
|
|
time), export of reserve map address to the asm file, ability to
|
|
specify reserve map content at compile time, etc...
|
|
|
|
We may provide a .h include file with common definitions of that
|
|
proves useful for some properties (like building PCI properties or
|
|
interrupt maps) though it may be better to add a notion of struct
|
|
definitions to the compiler...
|
|
|
|
|
|
V - Recommendations for a bootloader
|
|
====================================
|
|
|
|
|
|
Here are some various ideas/recommendations that have been proposed
|
|
while all this has been defined and implemented.
|
|
|
|
- The bootloader may want to be able to use the device-tree itself
|
|
and may want to manipulate it (to add/edit some properties,
|
|
like physical memory size or kernel arguments). At this point, 2
|
|
choices can be made. Either the bootloader works directly on the
|
|
flattened format, or the bootloader has its own internal tree
|
|
representation with pointers (similar to the kernel one) and
|
|
re-flattens the tree when booting the kernel. The former is a bit
|
|
more difficult to edit/modify, the later requires probably a bit
|
|
more code to handle the tree structure. Note that the structure
|
|
format has been designed so it's relatively easy to "insert"
|
|
properties or nodes or delete them by just memmoving things
|
|
around. It contains no internal offsets or pointers for this
|
|
purpose.
|
|
|
|
- An example of code for iterating nodes & retrieving properties
|
|
directly from the flattened tree format can be found in the kernel
|
|
file arch/ppc64/kernel/prom.c, look at scan_flat_dt() function,
|
|
its usage in early_init_devtree(), and the corresponding various
|
|
early_init_dt_scan_*() callbacks. That code can be re-used in a
|
|
GPL bootloader, and as the author of that code, I would be happy
|
|
to discuss possible free licensing to any vendor who wishes to
|
|
integrate all or part of this code into a non-GPL bootloader.
|
|
|
|
|
|
|
|
VI - System-on-a-chip devices and nodes
|
|
=======================================
|
|
|
|
Many companies are now starting to develop system-on-a-chip
|
|
processors, where the processor core (CPU) and many peripheral devices
|
|
exist on a single piece of silicon. For these SOCs, an SOC node
|
|
should be used that defines child nodes for the devices that make
|
|
up the SOC. While platforms are not required to use this model in
|
|
order to boot the kernel, it is highly encouraged that all SOC
|
|
implementations define as complete a flat-device-tree as possible to
|
|
describe the devices on the SOC. This will allow for the
|
|
genericization of much of the kernel code.
|
|
|
|
|
|
1) Defining child nodes of an SOC
|
|
---------------------------------
|
|
|
|
Each device that is part of an SOC may have its own node entry inside
|
|
the SOC node. For each device that is included in the SOC, the unit
|
|
address property represents the address offset for this device's
|
|
memory-mapped registers in the parent's address space. The parent's
|
|
address space is defined by the "ranges" property in the top-level soc
|
|
node. The "reg" property for each node that exists directly under the
|
|
SOC node should contain the address mapping from the child address space
|
|
to the parent SOC address space and the size of the device's
|
|
memory-mapped register file.
|
|
|
|
For many devices that may exist inside an SOC, there are predefined
|
|
specifications for the format of the device tree node. All SOC child
|
|
nodes should follow these specifications, except where noted in this
|
|
document.
|
|
|
|
See appendix A for an example partial SOC node definition for the
|
|
MPC8540.
|
|
|
|
|
|
2) Representing devices without a current OF specification
|
|
----------------------------------------------------------
|
|
|
|
Currently, there are many devices on SOCs that do not have a standard
|
|
representation pre-defined as part of the open firmware
|
|
specifications, mainly because the boards that contain these SOCs are
|
|
not currently booted using open firmware. This section contains
|
|
descriptions for the SOC devices for which new nodes have been
|
|
defined; this list will expand as more and more SOC-containing
|
|
platforms are moved over to use the flattened-device-tree model.
|
|
|
|
VII - Specifying interrupt information for devices
|
|
===================================================
|
|
|
|
The device tree represents the busses and devices of a hardware
|
|
system in a form similar to the physical bus topology of the
|
|
hardware.
|
|
|
|
In addition, a logical 'interrupt tree' exists which represents the
|
|
hierarchy and routing of interrupts in the hardware.
|
|
|
|
The interrupt tree model is fully described in the
|
|
document "Open Firmware Recommended Practice: Interrupt
|
|
Mapping Version 0.9". The document is available at:
|
|
<http://playground.sun.com/1275/practice>.
|
|
|
|
1) interrupts property
|
|
----------------------
|
|
|
|
Devices that generate interrupts to a single interrupt controller
|
|
should use the conventional OF representation described in the
|
|
OF interrupt mapping documentation.
|
|
|
|
Each device which generates interrupts must have an 'interrupt'
|
|
property. The interrupt property value is an arbitrary number of
|
|
of 'interrupt specifier' values which describe the interrupt or
|
|
interrupts for the device.
|
|
|
|
The encoding of an interrupt specifier is determined by the
|
|
interrupt domain in which the device is located in the
|
|
interrupt tree. The root of an interrupt domain specifies in
|
|
its #interrupt-cells property the number of 32-bit cells
|
|
required to encode an interrupt specifier. See the OF interrupt
|
|
mapping documentation for a detailed description of domains.
|
|
|
|
For example, the binding for the OpenPIC interrupt controller
|
|
specifies an #interrupt-cells value of 2 to encode the interrupt
|
|
number and level/sense information. All interrupt children in an
|
|
OpenPIC interrupt domain use 2 cells per interrupt in their interrupts
|
|
property.
|
|
|
|
The PCI bus binding specifies a #interrupt-cell value of 1 to encode
|
|
which interrupt pin (INTA,INTB,INTC,INTD) is used.
|
|
|
|
2) interrupt-parent property
|
|
----------------------------
|
|
|
|
The interrupt-parent property is specified to define an explicit
|
|
link between a device node and its interrupt parent in
|
|
the interrupt tree. The value of interrupt-parent is the
|
|
phandle of the parent node.
|
|
|
|
If the interrupt-parent property is not defined for a node, its
|
|
interrupt parent is assumed to be an ancestor in the node's
|
|
_device tree_ hierarchy.
|
|
|
|
3) OpenPIC Interrupt Controllers
|
|
--------------------------------
|
|
|
|
OpenPIC interrupt controllers require 2 cells to encode
|
|
interrupt information. The first cell defines the interrupt
|
|
number. The second cell defines the sense and level
|
|
information.
|
|
|
|
Sense and level information should be encoded as follows:
|
|
|
|
0 = low to high edge sensitive type enabled
|
|
1 = active low level sensitive type enabled
|
|
2 = active high level sensitive type enabled
|
|
3 = high to low edge sensitive type enabled
|
|
|
|
4) ISA Interrupt Controllers
|
|
----------------------------
|
|
|
|
ISA PIC interrupt controllers require 2 cells to encode
|
|
interrupt information. The first cell defines the interrupt
|
|
number. The second cell defines the sense and level
|
|
information.
|
|
|
|
ISA PIC interrupt controllers should adhere to the ISA PIC
|
|
encodings listed below:
|
|
|
|
0 = active low level sensitive type enabled
|
|
1 = active high level sensitive type enabled
|
|
2 = high to low edge sensitive type enabled
|
|
3 = low to high edge sensitive type enabled
|
|
|
|
VIII - Specifying Device Power Management Information (sleep property)
|
|
===================================================================
|
|
|
|
Devices on SOCs often have mechanisms for placing devices into low-power
|
|
states that are decoupled from the devices' own register blocks. Sometimes,
|
|
this information is more complicated than a cell-index property can
|
|
reasonably describe. Thus, each device controlled in such a manner
|
|
may contain a "sleep" property which describes these connections.
|
|
|
|
The sleep property consists of one or more sleep resources, each of
|
|
which consists of a phandle to a sleep controller, followed by a
|
|
controller-specific sleep specifier of zero or more cells.
|
|
|
|
The semantics of what type of low power modes are possible are defined
|
|
by the sleep controller. Some examples of the types of low power modes
|
|
that may be supported are:
|
|
|
|
- Dynamic: The device may be disabled or enabled at any time.
|
|
- System Suspend: The device may request to be disabled or remain
|
|
awake during system suspend, but will not be disabled until then.
|
|
- Permanent: The device is disabled permanently (until the next hard
|
|
reset).
|
|
|
|
Some devices may share a clock domain with each other, such that they should
|
|
only be suspended when none of the devices are in use. Where reasonable,
|
|
such nodes should be placed on a virtual bus, where the bus has the sleep
|
|
property. If the clock domain is shared among devices that cannot be
|
|
reasonably grouped in this manner, then create a virtual sleep controller
|
|
(similar to an interrupt nexus, except that defining a standardized
|
|
sleep-map should wait until its necessity is demonstrated).
|
|
|
|
Appendix A - Sample SOC node for MPC8540
|
|
========================================
|
|
|
|
soc@e0000000 {
|
|
#address-cells = <1>;
|
|
#size-cells = <1>;
|
|
compatible = "fsl,mpc8540-ccsr", "simple-bus";
|
|
device_type = "soc";
|
|
ranges = <0x00000000 0xe0000000 0x00100000>
|
|
bus-frequency = <0>;
|
|
interrupt-parent = <&pic>;
|
|
|
|
ethernet@24000 {
|
|
#address-cells = <1>;
|
|
#size-cells = <1>;
|
|
device_type = "network";
|
|
model = "TSEC";
|
|
compatible = "gianfar", "simple-bus";
|
|
reg = <0x24000 0x1000>;
|
|
local-mac-address = [ 00 E0 0C 00 73 00 ];
|
|
interrupts = <29 2 30 2 34 2>;
|
|
phy-handle = <&phy0>;
|
|
sleep = <&pmc 00000080>;
|
|
ranges;
|
|
|
|
mdio@24520 {
|
|
reg = <0x24520 0x20>;
|
|
compatible = "fsl,gianfar-mdio";
|
|
|
|
phy0: ethernet-phy@0 {
|
|
interrupts = <5 1>;
|
|
reg = <0>;
|
|
device_type = "ethernet-phy";
|
|
};
|
|
|
|
phy1: ethernet-phy@1 {
|
|
interrupts = <5 1>;
|
|
reg = <1>;
|
|
device_type = "ethernet-phy";
|
|
};
|
|
|
|
phy3: ethernet-phy@3 {
|
|
interrupts = <7 1>;
|
|
reg = <3>;
|
|
device_type = "ethernet-phy";
|
|
};
|
|
};
|
|
};
|
|
|
|
ethernet@25000 {
|
|
device_type = "network";
|
|
model = "TSEC";
|
|
compatible = "gianfar";
|
|
reg = <0x25000 0x1000>;
|
|
local-mac-address = [ 00 E0 0C 00 73 01 ];
|
|
interrupts = <13 2 14 2 18 2>;
|
|
phy-handle = <&phy1>;
|
|
sleep = <&pmc 00000040>;
|
|
};
|
|
|
|
ethernet@26000 {
|
|
device_type = "network";
|
|
model = "FEC";
|
|
compatible = "gianfar";
|
|
reg = <0x26000 0x1000>;
|
|
local-mac-address = [ 00 E0 0C 00 73 02 ];
|
|
interrupts = <41 2>;
|
|
phy-handle = <&phy3>;
|
|
sleep = <&pmc 00000020>;
|
|
};
|
|
|
|
serial@4500 {
|
|
#address-cells = <1>;
|
|
#size-cells = <1>;
|
|
compatible = "fsl,mpc8540-duart", "simple-bus";
|
|
sleep = <&pmc 00000002>;
|
|
ranges;
|
|
|
|
serial@4500 {
|
|
device_type = "serial";
|
|
compatible = "ns16550";
|
|
reg = <0x4500 0x100>;
|
|
clock-frequency = <0>;
|
|
interrupts = <42 2>;
|
|
};
|
|
|
|
serial@4600 {
|
|
device_type = "serial";
|
|
compatible = "ns16550";
|
|
reg = <0x4600 0x100>;
|
|
clock-frequency = <0>;
|
|
interrupts = <42 2>;
|
|
};
|
|
};
|
|
|
|
pic: pic@40000 {
|
|
interrupt-controller;
|
|
#address-cells = <0>;
|
|
#interrupt-cells = <2>;
|
|
reg = <0x40000 0x40000>;
|
|
compatible = "chrp,open-pic";
|
|
device_type = "open-pic";
|
|
};
|
|
|
|
i2c@3000 {
|
|
interrupts = <43 2>;
|
|
reg = <0x3000 0x100>;
|
|
compatible = "fsl-i2c";
|
|
dfsrr;
|
|
sleep = <&pmc 00000004>;
|
|
};
|
|
|
|
pmc: power@e0070 {
|
|
compatible = "fsl,mpc8540-pmc", "fsl,mpc8548-pmc";
|
|
reg = <0xe0070 0x20>;
|
|
};
|
|
};
|