Documentation/scsi/ufs.txt

   1                        Universal Flash Storage
   2                        =======================
   3
   4
   5 Contents
   6 --------
   7
   8 1. Overview
   9 2. UFS Architecture Overview
  10   2.1 Application Layer
  11   2.2 UFS Transport Protocol(UTP) layer
  12   2.3 UFS Interconnect(UIC) Layer
  13 3. 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
  18
  19
  20 1. Overview
  21 -----------
  22
  23 Universal Flash Storage(UFS) is a storage specification for flash devices.
  24 It is aimed to provide a universal storage interface for both
  25 embedded and removable flash memory based storage in mobile
  26 devices such as smart phones and tablet computers. The specification
  27 is defined by JEDEC Solid State Technology Association. UFS is based
  28 on MIPI M-PHY physical layer standard. UFS uses MIPI M-PHY as the
  29 physical layer and MIPI Unipro as the link layer.
  30
  31 The 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
  40
  41
  42 2. UFS Architecture Overview
  43 ----------------------------
  44
  45 UFS has a layered communication architecture which is based on SCSI
  46 SAM-5 architectural model.
  47
  48 UFS communication architecture consists of following layers,
  49
  50 2.1 Application Layer
  51
  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.
  66
  67 2.2 UFS Transport Protocol(UTP) layer
  68
  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).
  80
  81 2.3 UFS Interconnect(UIC) Layer
  82
  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.
  89
  90
  91 3. UFSHCD Overview
  92 ------------------
  93
  94 The UFS host controller driver is based on Linux SCSI Framework.
  95 UFSHCD is a low level device driver which acts as an interface between
  96 SCSI Midlayer and PCIe based UFS host controllers.
  97
  98 The current UFSHCD implementation supports following functionality,
  99
 100 3.1 UFS controller initialization
 101
 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.
 105
 106 3.2 UTP Transfer requests
 107
 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.
 113
 114 3.3 UFS error handling
 115
 116   Error handling module handles Host controller fatal errors,
 117   Device fatal errors and UIC interconnect layer related errors.
 118
 119 3.4 SCSI Error handling
 120
 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.
 127
 128 In this version of UFSHCD Query requests and power management
 129 functionality are not implemented.
 130
 131 UFS Specifications can be found at,
 132 UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf
 133 UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf