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- 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