1                       Universal Flash Storage
   2                       =======================
   81. Overview
   92. UFS Architecture Overview
  10  2.1 Application Layer
  11  2.2 UFS Transport Protocol(UTP) layer
  12  2.3 UFS Interconnect(UIC) Layer
  133. UFSHCD Overview
  14  3.1 UFS controller initialization
  15  3.2 UTP Transfer requests
  16  3.3 UFS error handling
  17  3.4 SCSI Error handling
  201. Overview
  23Universal Flash Storage(UFS) is a storage specification for flash devices.
  24It is aimed to provide a universal storage interface for both
  25embedded and removable flash memory based storage in mobile
  26devices such as smart phones and tablet computers. The specification
  27is defined by JEDEC Solid State Technology Association. UFS is based
  28on MIPI M-PHY physical layer standard. UFS uses MIPI M-PHY as the
  29physical layer and MIPI Unipro as the link layer.
  31The main goals of UFS is to provide,
  32 * Optimized performance:
  33   For UFS version 1.0 and 1.1 the target performance is as follows,
  34   Support for Gear1 is mandatory (rate A: 1248Mbps, rate B: 1457.6Mbps)
  35   Support for Gear2 is optional (rate A: 2496Mbps, rate B: 2915.2Mbps)
  36   Future version of the standard,
  37   Gear3 (rate A: 4992Mbps, rate B: 5830.4Mbps)
  38 * Low power consumption
  39 * High random IOPs and low latency
  422. UFS Architecture Overview
  45UFS has a layered communication architecture which is based on SCSI
  46SAM-5 architectural model.
  48UFS communication architecture consists of following layers,
  502.1 Application Layer
  52  The Application layer is composed of UFS command set layer(UCS),
  53  Task Manager and Device manager. The UFS interface is designed to be
  54  protocol agnostic, however SCSI has been selected as a baseline
  55  protocol for versions 1.0 and 1.1 of UFS protocol  layer.
  56  UFS supports subset of SCSI commands defined by SPC-4 and SBC-3.
  57  * UCS: It handles SCSI commands supported by UFS specification.
  58  * Task manager: It handles task management functions defined by the
  59     UFS which are meant for command queue control.
  60  * Device manager: It handles device level operations and device
  61     configuration operations. Device level operations mainly involve
  62     device power management operations and commands to Interconnect
  63     layers. Device level configurations involve handling of query
  64     requests which are used to modify and retrieve configuration
  65     information of the device.
  672.2 UFS Transport Protocol(UTP) layer
  69  UTP layer provides services for
  70  the higher layers through Service Access Points. UTP defines 3
  71  service access points for higher layers.
  72  * UDM_SAP: Device manager service access point is exposed to device
  73    manager for device level operations. These device level operations
  74    are done through query requests.
  75  * UTP_CMD_SAP: Command service access point is exposed to UFS command
  76    set layer(UCS) to transport commands.
  77  * UTP_TM_SAP: Task management service access point is exposed to task
  78    manager to transport task management functions.
  79  UTP transports messages through UFS protocol information unit(UPIU).
  812.3 UFS Interconnect(UIC) Layer
  83  UIC is the lowest layer of UFS layered architecture. It handles
  84  connection between UFS host and UFS device. UIC consists of
  85  MIPI UniPro and MIPI M-PHY. UIC provides 2 service access points
  86  to upper layer,
  87  * UIC_SAP: To transport UPIU between UFS host and UFS device.
  88  * UIO_SAP: To issue commands to Unipro layers.
  913. UFSHCD Overview
  94The UFS host controller driver is based on Linux SCSI Framework.
  95UFSHCD is a low level device driver which acts as an interface between
  96SCSI Midlayer and PCIe based UFS host controllers.
  98The current UFSHCD implementation supports following functionality,
 1003.1 UFS controller initialization
 102  The initialization module brings UFS host controller to active state
 103  and prepares the controller to transfer commands/response between
 104  UFSHCD and UFS device.
 1063.2 UTP Transfer requests
 108  Transfer request handling module of UFSHCD receives SCSI commands
 109  from SCSI Midlayer, forms UPIUs and issues the UPIUs to UFS Host
 110  controller. Also, the module decodes, responses received from UFS
 111  host controller in the form of UPIUs and intimates the SCSI Midlayer
 112  of the status of the command.
 1143.3 UFS error handling
 116  Error handling module handles Host controller fatal errors,
 117  Device fatal errors and UIC interconnect layer related errors.
 1193.4 SCSI Error handling
 121  This is done through UFSHCD SCSI error handling routines registered
 122  with SCSI Midlayer. Examples of some of the error handling commands
 123  issues by SCSI Midlayer are Abort task, Lun reset and host reset.
 124  UFSHCD Routines to perform these tasks are registered with
 125  SCSI Midlayer through .eh_abort_handler, .eh_device_reset_handler and
 126  .eh_host_reset_handler.
 128In this version of UFSHCD Query requests and power management
 129functionality are not implemented.
 131UFS Specifications can be found at,
 132UFS -
 133UFSHCI -
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