forked from Minki/linux
7ade8495dc
The latest Xilinx design tools called ISE and EDK has been released in October 2013. New tool doesn't support any PPC405/PPC440 new designs. These platforms are no longer supported and tested. PowerPC 405/440 port is orphan from 2013 by commitcdeb89943b("MAINTAINERS: Fix incorrect status tag") and commit19624236cc("MAINTAINERS: Update Grant's email address and maintainership") that's why it is time to remove the support fot these platforms. Signed-off-by: Michal Simek <michal.simek@xilinx.com> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Acked-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/8c593895e2cb57d232d85ce4d8c3a1aa7f0869cc.1590079968.git.christophe.leroy@csgroup.eu
132 lines
6.6 KiB
ReStructuredText
132 lines
6.6 KiB
ReStructuredText
========================
|
|
The PowerPC boot wrapper
|
|
========================
|
|
|
|
Copyright (C) Secret Lab Technologies Ltd.
|
|
|
|
PowerPC image targets compresses and wraps the kernel image (vmlinux) with
|
|
a boot wrapper to make it usable by the system firmware. There is no
|
|
standard PowerPC firmware interface, so the boot wrapper is designed to
|
|
be adaptable for each kind of image that needs to be built.
|
|
|
|
The boot wrapper can be found in the arch/powerpc/boot/ directory. The
|
|
Makefile in that directory has targets for all the available image types.
|
|
The different image types are used to support all of the various firmware
|
|
interfaces found on PowerPC platforms. OpenFirmware is the most commonly
|
|
used firmware type on general purpose PowerPC systems from Apple, IBM and
|
|
others. U-Boot is typically found on embedded PowerPC hardware, but there
|
|
are a handful of other firmware implementations which are also popular. Each
|
|
firmware interface requires a different image format.
|
|
|
|
The boot wrapper is built from the makefile in arch/powerpc/boot/Makefile and
|
|
it uses the wrapper script (arch/powerpc/boot/wrapper) to generate target
|
|
image. The details of the build system is discussed in the next section.
|
|
Currently, the following image format targets exist:
|
|
|
|
==================== ========================================================
|
|
cuImage.%: Backwards compatible uImage for older version of
|
|
U-Boot (for versions that don't understand the device
|
|
tree). This image embeds a device tree blob inside
|
|
the image. The boot wrapper, kernel and device tree
|
|
are all embedded inside the U-Boot uImage file format
|
|
with boot wrapper code that extracts data from the old
|
|
bd_info structure and loads the data into the device
|
|
tree before jumping into the kernel.
|
|
|
|
Because of the series of #ifdefs found in the
|
|
bd_info structure used in the old U-Boot interfaces,
|
|
cuImages are platform specific. Each specific
|
|
U-Boot platform has a different platform init file
|
|
which populates the embedded device tree with data
|
|
from the platform specific bd_info file. The platform
|
|
specific cuImage platform init code can be found in
|
|
`arch/powerpc/boot/cuboot.*.c`. Selection of the correct
|
|
cuImage init code for a specific board can be found in
|
|
the wrapper structure.
|
|
|
|
dtbImage.%: Similar to zImage, except device tree blob is embedded
|
|
inside the image instead of provided by firmware. The
|
|
output image file can be either an elf file or a flat
|
|
binary depending on the platform.
|
|
|
|
dtbImages are used on systems which do not have an
|
|
interface for passing a device tree directly.
|
|
dtbImages are similar to simpleImages except that
|
|
dtbImages have platform specific code for extracting
|
|
data from the board firmware, but simpleImages do not
|
|
talk to the firmware at all.
|
|
|
|
PlayStation 3 support uses dtbImage. So do Embedded
|
|
Planet boards using the PlanetCore firmware. Board
|
|
specific initialization code is typically found in a
|
|
file named arch/powerpc/boot/<platform>.c; but this
|
|
can be overridden by the wrapper script.
|
|
|
|
simpleImage.%: Firmware independent compressed image that does not
|
|
depend on any particular firmware interface and embeds
|
|
a device tree blob. This image is a flat binary that
|
|
can be loaded to any location in RAM and jumped to.
|
|
Firmware cannot pass any configuration data to the
|
|
kernel with this image type and it depends entirely on
|
|
the embedded device tree for all information.
|
|
|
|
treeImage.%; Image format for used with OpenBIOS firmware found
|
|
on some ppc4xx hardware. This image embeds a device
|
|
tree blob inside the image.
|
|
|
|
uImage: Native image format used by U-Boot. The uImage target
|
|
does not add any boot code. It just wraps a compressed
|
|
vmlinux in the uImage data structure. This image
|
|
requires a version of U-Boot that is able to pass
|
|
a device tree to the kernel at boot. If using an older
|
|
version of U-Boot, then you need to use a cuImage
|
|
instead.
|
|
|
|
zImage.%: Image format which does not embed a device tree.
|
|
Used by OpenFirmware and other firmware interfaces
|
|
which are able to supply a device tree. This image
|
|
expects firmware to provide the device tree at boot.
|
|
Typically, if you have general purpose PowerPC
|
|
hardware then you want this image format.
|
|
==================== ========================================================
|
|
|
|
Image types which embed a device tree blob (simpleImage, dtbImage, treeImage,
|
|
and cuImage) all generate the device tree blob from a file in the
|
|
arch/powerpc/boot/dts/ directory. The Makefile selects the correct device
|
|
tree source based on the name of the target. Therefore, if the kernel is
|
|
built with 'make treeImage.walnut', then the build system will use
|
|
arch/powerpc/boot/dts/walnut.dts to build treeImage.walnut.
|
|
|
|
Two special targets called 'zImage' and 'zImage.initrd' also exist. These
|
|
targets build all the default images as selected by the kernel configuration.
|
|
Default images are selected by the boot wrapper Makefile
|
|
(arch/powerpc/boot/Makefile) by adding targets to the $image-y variable. Look
|
|
at the Makefile to see which default image targets are available.
|
|
|
|
How it is built
|
|
---------------
|
|
arch/powerpc is designed to support multiplatform kernels, which means
|
|
that a single vmlinux image can be booted on many different target boards.
|
|
It also means that the boot wrapper must be able to wrap for many kinds of
|
|
images on a single build. The design decision was made to not use any
|
|
conditional compilation code (#ifdef, etc) in the boot wrapper source code.
|
|
All of the boot wrapper pieces are buildable at any time regardless of the
|
|
kernel configuration. Building all the wrapper bits on every kernel build
|
|
also ensures that obscure parts of the wrapper are at the very least compile
|
|
tested in a large variety of environments.
|
|
|
|
The wrapper is adapted for different image types at link time by linking in
|
|
just the wrapper bits that are appropriate for the image type. The 'wrapper
|
|
script' (found in arch/powerpc/boot/wrapper) is called by the Makefile and
|
|
is responsible for selecting the correct wrapper bits for the image type.
|
|
The arguments are well documented in the script's comment block, so they
|
|
are not repeated here. However, it is worth mentioning that the script
|
|
uses the -p (platform) argument as the main method of deciding which wrapper
|
|
bits to compile in. Look for the large 'case "$platform" in' block in the
|
|
middle of the script. This is also the place where platform specific fixups
|
|
can be selected by changing the link order.
|
|
|
|
In particular, care should be taken when working with cuImages. cuImage
|
|
wrapper bits are very board specific and care should be taken to make sure
|
|
the target you are trying to build is supported by the wrapper bits.
|