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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