mirror of
https://github.com/torvalds/linux.git
synced 2024-12-11 13:41:55 +00:00
cf065a7da5
Correct spelling problems for Documentation/scsi/ as reported by codespell. Link: https://lore.kernel.org/r/20230129231053.20863-8-rdunlap@infradead.org Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: linux-doc@vger.kernel.org Cc: "James E.J. Bottomley" <jejb@linux.ibm.com> Cc: "Martin K. Petersen" <martin.petersen@oracle.com> Cc: linux-scsi@vger.kernel.org Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
211 lines
7.5 KiB
ReStructuredText
211 lines
7.5 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
=======================
|
|
Universal Flash Storage
|
|
=======================
|
|
|
|
|
|
.. Contents
|
|
|
|
1. Overview
|
|
2. UFS Architecture Overview
|
|
2.1 Application Layer
|
|
2.2 UFS Transport Protocol (UTP) layer
|
|
2.3 UFS Interconnect (UIC) Layer
|
|
3. UFSHCD Overview
|
|
3.1 UFS controller initialization
|
|
3.2 UTP Transfer requests
|
|
3.3 UFS error handling
|
|
3.4 SCSI Error handling
|
|
4. BSG Support
|
|
5. UFS Reference Clock Frequency configuration
|
|
|
|
|
|
1. Overview
|
|
===========
|
|
|
|
Universal Flash Storage (UFS) is a storage specification for flash devices.
|
|
It aims to provide a universal storage interface for both
|
|
embedded and removable flash memory-based storage in mobile
|
|
devices such as smart phones and tablet computers. The specification
|
|
is defined by JEDEC Solid State Technology Association. UFS is based
|
|
on the MIPI M-PHY physical layer standard. UFS uses MIPI M-PHY as the
|
|
physical layer and MIPI Unipro as the link layer.
|
|
|
|
The main goals of UFS are to provide:
|
|
|
|
* Optimized performance:
|
|
|
|
For UFS version 1.0 and 1.1 the target performance is as follows:
|
|
|
|
- Support for Gear1 is mandatory (rate A: 1248Mbps, rate B: 1457.6Mbps)
|
|
- Support for Gear2 is optional (rate A: 2496Mbps, rate B: 2915.2Mbps)
|
|
|
|
Future version of the standard,
|
|
|
|
- Gear3 (rate A: 4992Mbps, rate B: 5830.4Mbps)
|
|
|
|
* Low power consumption
|
|
* High random IOPs and low latency
|
|
|
|
|
|
2. UFS Architecture Overview
|
|
============================
|
|
|
|
UFS has a layered communication architecture which is based on SCSI
|
|
SAM-5 architectural model.
|
|
|
|
UFS communication architecture consists of the following layers.
|
|
|
|
2.1 Application Layer
|
|
---------------------
|
|
|
|
The Application layer is composed of the UFS command set layer (UCS),
|
|
Task Manager and Device manager. The UFS interface is designed to be
|
|
protocol agnostic, however SCSI has been selected as a baseline
|
|
protocol for versions 1.0 and 1.1 of the UFS protocol layer.
|
|
|
|
UFS supports a subset of SCSI commands defined by SPC-4 and SBC-3.
|
|
|
|
* UCS:
|
|
It handles SCSI commands supported by UFS specification.
|
|
* Task manager:
|
|
It handles task management functions defined by the
|
|
UFS which are meant for command queue control.
|
|
* Device manager:
|
|
It handles device level operations and device
|
|
configuration operations. Device level operations mainly involve
|
|
device power management operations and commands to Interconnect
|
|
layers. Device level configurations involve handling of query
|
|
requests which are used to modify and retrieve configuration
|
|
information of the device.
|
|
|
|
2.2 UFS Transport Protocol (UTP) layer
|
|
--------------------------------------
|
|
|
|
The UTP layer provides services for
|
|
the higher layers through Service Access Points. UTP defines 3
|
|
service access points for higher layers.
|
|
|
|
* UDM_SAP: Device manager service access point is exposed to device
|
|
manager for device level operations. These device level operations
|
|
are done through query requests.
|
|
* UTP_CMD_SAP: Command service access point is exposed to UFS command
|
|
set layer (UCS) to transport commands.
|
|
* UTP_TM_SAP: Task management service access point is exposed to task
|
|
manager to transport task management functions.
|
|
|
|
UTP transports messages through UFS protocol information unit (UPIU).
|
|
|
|
2.3 UFS Interconnect (UIC) Layer
|
|
--------------------------------
|
|
|
|
UIC is the lowest layer of the UFS layered architecture. It handles
|
|
the connection between UFS host and UFS device. UIC consists of
|
|
MIPI UniPro and MIPI M-PHY. UIC provides 2 service access points
|
|
to upper layer:
|
|
|
|
* UIC_SAP: To transport UPIU between UFS host and UFS device.
|
|
* UIO_SAP: To issue commands to Unipro layers.
|
|
|
|
|
|
3. UFSHCD Overview
|
|
==================
|
|
|
|
The UFS host controller driver is based on the Linux SCSI Framework.
|
|
UFSHCD is a low-level device driver which acts as an interface between
|
|
the SCSI Midlayer and PCIe-based UFS host controllers.
|
|
|
|
The current UFSHCD implementation supports the following functionality:
|
|
|
|
3.1 UFS controller initialization
|
|
---------------------------------
|
|
|
|
The initialization module brings the UFS host controller to active state
|
|
and prepares the controller to transfer commands/responses between
|
|
UFSHCD and UFS device.
|
|
|
|
3.2 UTP Transfer requests
|
|
-------------------------
|
|
|
|
Transfer request handling module of UFSHCD receives SCSI commands
|
|
from the SCSI Midlayer, forms UPIUs and issues the UPIUs to the UFS Host
|
|
controller. Also, the module decodes responses received from the UFS
|
|
host controller in the form of UPIUs and intimates the SCSI Midlayer
|
|
of the status of the command.
|
|
|
|
3.3 UFS error handling
|
|
----------------------
|
|
|
|
Error handling module handles Host controller fatal errors,
|
|
Device fatal errors and UIC interconnect layer-related errors.
|
|
|
|
3.4 SCSI Error handling
|
|
-----------------------
|
|
|
|
This is done through UFSHCD SCSI error handling routines registered
|
|
with the SCSI Midlayer. Examples of some of the error handling commands
|
|
issues by the SCSI Midlayer are Abort task, LUN reset and host reset.
|
|
UFSHCD Routines to perform these tasks are registered with
|
|
SCSI Midlayer through .eh_abort_handler, .eh_device_reset_handler and
|
|
.eh_host_reset_handler.
|
|
|
|
In this version of UFSHCD, Query requests and power management
|
|
functionality are not implemented.
|
|
|
|
4. BSG Support
|
|
==============
|
|
|
|
This transport driver supports exchanging UFS protocol information units
|
|
(UPIUs) with a UFS device. Typically, user space will allocate
|
|
struct ufs_bsg_request and struct ufs_bsg_reply (see ufs_bsg.h) as
|
|
request_upiu and reply_upiu respectively. Filling those UPIUs should
|
|
be done in accordance with JEDEC spec UFS2.1 paragraph 10.7.
|
|
*Caveat emptor*: The driver makes no further input validations and sends the
|
|
UPIU to the device as it is. Open the bsg device in /dev/ufs-bsg and
|
|
send SG_IO with the applicable sg_io_v4::
|
|
|
|
io_hdr_v4.guard = 'Q';
|
|
io_hdr_v4.protocol = BSG_PROTOCOL_SCSI;
|
|
io_hdr_v4.subprotocol = BSG_SUB_PROTOCOL_SCSI_TRANSPORT;
|
|
io_hdr_v4.response = (__u64)reply_upiu;
|
|
io_hdr_v4.max_response_len = reply_len;
|
|
io_hdr_v4.request_len = request_len;
|
|
io_hdr_v4.request = (__u64)request_upiu;
|
|
if (dir == SG_DXFER_TO_DEV) {
|
|
io_hdr_v4.dout_xfer_len = (uint32_t)byte_cnt;
|
|
io_hdr_v4.dout_xferp = (uintptr_t)(__u64)buff;
|
|
} else {
|
|
io_hdr_v4.din_xfer_len = (uint32_t)byte_cnt;
|
|
io_hdr_v4.din_xferp = (uintptr_t)(__u64)buff;
|
|
}
|
|
|
|
If you wish to read or write a descriptor, use the appropriate xferp of
|
|
sg_io_v4.
|
|
|
|
The userspace tool that interacts with the ufs-bsg endpoint and uses its
|
|
UPIU-based protocol is available at:
|
|
|
|
https://github.com/westerndigitalcorporation/ufs-tool
|
|
|
|
For more detailed information about the tool and its supported
|
|
features, please see the tool's README.
|
|
|
|
UFS specifications can be found at:
|
|
|
|
- UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf
|
|
- UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf
|
|
|
|
5. UFS Reference Clock Frequency configuration
|
|
==============================================
|
|
|
|
Devicetree can define a clock named "ref_clk" under the UFS controller node
|
|
to specify the intended reference clock frequency for the UFS storage
|
|
parts. ACPI-based system can specify the frequency using ACPI
|
|
Device-Specific Data property named "ref-clk-freq". In both ways the value
|
|
is interpreted as frequency in Hz and must match one of the values given in
|
|
the UFS specification. UFS subsystem will attempt to read the value when
|
|
executing common controller initialization. If the value is available, UFS
|
|
subsystem will ensure the bRefClkFreq attribute of the UFS storage device is
|
|
set accordingly and will modify it if there is a mismatch.
|