1.. SPDX-License-Identifier: GPL-2.0 2 3======================= 4Universal Flash Storage 5======================= 6 7 8.. Contents 9 10 1. Overview 11 2. UFS Architecture Overview 12 2.1 Application Layer 13 2.2 UFS Transport Protocol (UTP) layer 14 2.3 UFS Interconnect (UIC) Layer 15 3. UFSHCD Overview 16 3.1 UFS controller initialization 17 3.2 UTP Transfer requests 18 3.3 UFS error handling 19 3.4 SCSI Error handling 20 4. BSG Support 21 5. UFS Reference Clock Frequency configuration 22 23 241. Overview 25=========== 26 27Universal Flash Storage (UFS) is a storage specification for flash devices. 28It aims to provide a universal storage interface for both 29embedded and removable flash memory-based storage in mobile 30devices such as smart phones and tablet computers. The specification 31is defined by JEDEC Solid State Technology Association. UFS is based 32on the MIPI M-PHY physical layer standard. UFS uses MIPI M-PHY as the 33physical layer and MIPI Unipro as the link layer. 34 35The main goals of UFS are to provide: 36 37 * Optimized performance: 38 39 For UFS version 1.0 and 1.1 the target performance is as follows: 40 41 - Support for Gear1 is mandatory (rate A: 1248Mbps, rate B: 1457.6Mbps) 42 - Support for Gear2 is optional (rate A: 2496Mbps, rate B: 2915.2Mbps) 43 44 Future version of the standard, 45 46 - Gear3 (rate A: 4992Mbps, rate B: 5830.4Mbps) 47 48 * Low power consumption 49 * High random IOPs and low latency 50 51 522. UFS Architecture Overview 53============================ 54 55UFS has a layered communication architecture which is based on SCSI 56SAM-5 architectural model. 57 58UFS communication architecture consists of the following layers. 59 602.1 Application Layer 61--------------------- 62 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 65 protocol agnostic, however SCSI has been selected as a baseline 66 protocol for versions 1.0 and 1.1 of the UFS protocol layer. 67 68 UFS supports a subset of SCSI commands defined by SPC-4 and SBC-3. 69 70 * UCS: 71 It handles SCSI commands supported by UFS specification. 72 * Task manager: 73 It handles task management functions defined by the 74 UFS which are meant for command queue control. 75 * Device manager: 76 It handles device level operations and device 77 configuration operations. Device level operations mainly involve 78 device power management operations and commands to Interconnect 79 layers. Device level configurations involve handling of query 80 requests which are used to modify and retrieve configuration 81 information of the device. 82 832.2 UFS Transport Protocol (UTP) layer 84-------------------------------------- 85 86 The UTP layer provides services for 87 the higher layers through Service Access Points. UTP defines 3 88 service access points for higher layers. 89 90 * UDM_SAP: Device manager service access point is exposed to device 91 manager for device level operations. These device level operations 92 are done through query requests. 93 * UTP_CMD_SAP: Command service access point is exposed to UFS command 94 set layer (UCS) to transport commands. 95 * UTP_TM_SAP: Task management service access point is exposed to task 96 manager to transport task management functions. 97 98 UTP transports messages through UFS protocol information unit (UPIU). 99 1002.3 UFS Interconnect (UIC) Layer 101-------------------------------- 102 103 UIC is the lowest layer of the UFS layered architecture. It handles 104 the connection between UFS host and UFS device. UIC consists of 105 MIPI UniPro and MIPI M-PHY. UIC provides 2 service access points 106 to upper layer: 107 108 * UIC_SAP: To transport UPIU between UFS host and UFS device. 109 * UIO_SAP: To issue commands to Unipro layers. 110 111 1123. UFSHCD Overview 113================== 114 115The UFS host controller driver is based on the Linux SCSI Framework. 116UFSHCD is a low-level device driver which acts as an interface between 117the SCSI Midlayer and PCIe-based UFS host controllers. 118 119The current UFSHCD implementation supports the following functionality: 120 1213.1 UFS controller initialization 122--------------------------------- 123 124 The initialization module brings the UFS host controller to active state 125 and prepares the controller to transfer commands/responses between 126 UFSHCD and UFS device. 127 1283.2 UTP Transfer requests 129------------------------- 130 131 Transfer request handling module of UFSHCD receives SCSI commands 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 134 host controller in the form of UPIUs and intimates the SCSI Midlayer 135 of the status of the command. 136 1373.3 UFS error handling 138---------------------- 139 140 Error handling module handles Host controller fatal errors, 141 Device fatal errors and UIC interconnect layer-related errors. 142 1433.4 SCSI Error handling 144----------------------- 145 146 This is done through UFSHCD SCSI error handling routines registered 147 with the SCSI Midlayer. Examples of some of the error handling commands 148 issues by the SCSI Midlayer are Abort task, LUN reset and host reset. 149 UFSHCD Routines to perform these tasks are registered with 150 SCSI Midlayer through .eh_abort_handler, .eh_device_reset_handler and 151 .eh_host_reset_handler. 152 153In this version of UFSHCD, Query requests and power management 154functionality are not implemented. 155 1564. BSG Support 157============== 158 159This transport driver supports exchanging UFS protocol information units 160(UPIUs) with a UFS device. Typically, user space will allocate 161struct ufs_bsg_request and struct ufs_bsg_reply (see ufs_bsg.h) as 162request_upiu and reply_upiu respectively. Filling those UPIUs should 163be done in accordance with JEDEC spec UFS2.1 paragraph 10.7. 164*Caveat emptor*: The driver makes no further input validations and sends the 165UPIU to the device as it is. Open the bsg device in /dev/ufs-bsg and 166send SG_IO with the applicable sg_io_v4:: 167 168 io_hdr_v4.guard = 'Q'; 169 io_hdr_v4.protocol = BSG_PROTOCOL_SCSI; 170 io_hdr_v4.subprotocol = BSG_SUB_PROTOCOL_SCSI_TRANSPORT; 171 io_hdr_v4.response = (__u64)reply_upiu; 172 io_hdr_v4.max_response_len = reply_len; 173 io_hdr_v4.request_len = request_len; 174 io_hdr_v4.request = (__u64)request_upiu; 175 if (dir == SG_DXFER_TO_DEV) { 176 io_hdr_v4.dout_xfer_len = (uint32_t)byte_cnt; 177 io_hdr_v4.dout_xferp = (uintptr_t)(__u64)buff; 178 } else { 179 io_hdr_v4.din_xfer_len = (uint32_t)byte_cnt; 180 io_hdr_v4.din_xferp = (uintptr_t)(__u64)buff; 181 } 182 183If you wish to read or write a descriptor, use the appropriate xferp of 184sg_io_v4. 185 186The userspace tool that interacts with the ufs-bsg endpoint and uses its 187UPIU-based protocol is available at: 188 189 https://github.com/westerndigitalcorporation/ufs-tool 190 191For more detailed information about the tool and its supported 192features, please see the tool's README. 193 194UFS specifications can be found at: 195 196- UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf 197- UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf 198 1995. UFS Reference Clock Frequency configuration 200============================================== 201 202Devicetree can define a clock named "ref_clk" under the UFS controller node 203to specify the intended reference clock frequency for the UFS storage 204parts. ACPI-based system can specify the frequency using ACPI 205Device-Specific Data property named "ref-clk-freq". In both ways the value 206is interpreted as frequency in Hz and must match one of the values given in 207the UFS specification. UFS subsystem will attempt to read the value when 208executing common controller initialization. If the value is available, UFS 209subsystem will ensure the bRefClkFreq attribute of the UFS storage device is 210set accordingly and will modify it if there is a mismatch. 211
