mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-12 13:55:32 +00:00
134 lines
5 KiB
Text
134 lines
5 KiB
Text
![]() |
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
|
||
|
|
||
|
|
||
|
1. Overview
|
||
|
-----------
|
||
|
|
||
|
Universal Flash Storage(UFS) is a storage specification for flash devices.
|
||
|
It is aimed 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 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 is 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 following layers,
|
||
|
|
||
|
2.1 Application Layer
|
||
|
|
||
|
The Application layer is composed of 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 UFS protocol layer.
|
||
|
UFS supports 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
|
||
|
|
||
|
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 UFS layered architecture. It handles
|
||
|
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 Linux SCSI Framework.
|
||
|
UFSHCD is a low level device driver which acts as an interface between
|
||
|
SCSI Midlayer and PCIe based UFS host controllers.
|
||
|
|
||
|
The current UFSHCD implementation supports following functionality,
|
||
|
|
||
|
3.1 UFS controller initialization
|
||
|
|
||
|
The initialization module brings UFS host controller to active state
|
||
|
and prepares the controller to transfer commands/response between
|
||
|
UFSHCD and UFS device.
|
||
|
|
||
|
3.2 UTP Transfer requests
|
||
|
|
||
|
Transfer request handling module of UFSHCD receives SCSI commands
|
||
|
from SCSI Midlayer, forms UPIUs and issues the UPIUs to UFS Host
|
||
|
controller. Also, the module decodes, responses received from 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 SCSI Midlayer. Examples of some of the error handling commands
|
||
|
issues by 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.
|
||
|
|
||
|
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
|