Documentation/scsi/ufs.rst

11    2. UFS Architecture Overview
13      2.2 UFS Transport Protocol (UTP) layer
14      2.3 UFS Interconnect (UIC) Layer
16      3.1 UFS controller initialization
18      3.3 UFS error handling
21    5. UFS Reference Clock Frequency configuration
27 Universal Flash Storage (UFS) is a storage specification for flash devices.
31 is defined by JEDEC Solid State Technology Association. UFS is based
32 on the MIPI M-PHY physical layer standard. UFS uses MIPI M-PHY as the
35 The main goals of UFS are to provide:
39    For UFS version 1.0 and 1.1 the target performance is as follows:
52 2. UFS Architecture Overview
55 UFS has a layered communication architecture which is based on SCSI
58 UFS communication architecture consists of the following layers.
63   The Application layer is composed of the UFS command set layer (UCS),
64   Task Manager and Device manager. The UFS interface is designed to be
66   protocol for versions 1.0 and 1.1 of the UFS protocol layer.
68   UFS supports a subset of SCSI commands defined by SPC-4 and SBC-3.
71      It handles SCSI commands supported by UFS specification.
74      UFS which are meant for command queue control.
83 2.2 UFS Transport Protocol (UTP) layer
93   * UTP_CMD_SAP: Command service access point is exposed to UFS command
98   UTP transports messages through UFS protocol information unit (UPIU).
100 2.3 UFS Interconnect (UIC) Layer
103   UIC is the lowest layer of the UFS layered architecture. It handles
104   the connection between UFS host and UFS device. UIC consists of
108   * UIC_SAP: To transport UPIU between UFS host and UFS device.
115 The UFS host controller driver is based on the Linux SCSI Framework.
117 the SCSI Midlayer and PCIe-based UFS host controllers.
121 3.1 UFS controller initialization
124   The initialization module brings the UFS host controller to active state
126   UFSHCD and UFS device.
132   from the SCSI Midlayer, forms UPIUs and issues the UPIUs to the UFS Host
133   controller. Also, the module decodes responses received from the UFS
137 3.3 UFS error handling
159 This transport driver supports exchanging UFS protocol information units
160 (UPIUs) with a UFS device. Typically, user space will allocate
165 UPIU to the device as it is.  Open the bsg device in /dev/ufs-bsg and
186 The userspace tool that interacts with the ufs-bsg endpoint and uses its
189 	https://github.com/westerndigitalcorporation/ufs-tool
194 UFS specifications can be found at:
196 - UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf
199 5. UFS Reference Clock Frequency configuration
202 Devicetree can define a clock named "ref_clk" under the UFS controller node
203 to specify the intended reference clock frequency for the UFS storage
207 the UFS specification. UFS subsystem will attempt to read the value when
208 executing common controller initialization. If the value is available, UFS
209 subsystem will ensure the bRefClkFreq attribute of the UFS storage device is