ufs.rst (6869B)
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 21 221. Overview 23=========== 24 25Universal Flash Storage (UFS) is a storage specification for flash devices. 26It aims to provide a universal storage interface for both 27embedded and removable flash memory-based storage in mobile 28devices such as smart phones and tablet computers. The specification 29is defined by JEDEC Solid State Technology Association. UFS is based 30on the MIPI M-PHY physical layer standard. UFS uses MIPI M-PHY as the 31physical layer and MIPI Unipro as the link layer. 32 33The main goals of UFS are to provide: 34 35 * Optimized performance: 36 37 For UFS version 1.0 and 1.1 the target performance is as follows: 38 39 - Support for Gear1 is mandatory (rate A: 1248Mbps, rate B: 1457.6Mbps) 40 - Support for Gear2 is optional (rate A: 2496Mbps, rate B: 2915.2Mbps) 41 42 Future version of the standard, 43 44 - Gear3 (rate A: 4992Mbps, rate B: 5830.4Mbps) 45 46 * Low power consumption 47 * High random IOPs and low latency 48 49 502. UFS Architecture Overview 51============================ 52 53UFS has a layered communication architecture which is based on SCSI 54SAM-5 architectural model. 55 56UFS communication architecture consists of the following layers. 57 582.1 Application Layer 59--------------------- 60 61 The Application layer is composed of the UFS command set layer (UCS), 62 Task Manager and Device manager. The UFS interface is designed to be 63 protocol agnostic, however SCSI has been selected as a baseline 64 protocol for versions 1.0 and 1.1 of the UFS protocol layer. 65 66 UFS supports a subset of SCSI commands defined by SPC-4 and SBC-3. 67 68 * UCS: 69 It handles SCSI commands supported by UFS specification. 70 * Task manager: 71 It handles task management functions defined by the 72 UFS which are meant for command queue control. 73 * Device manager: 74 It handles device level operations and device 75 configuration operations. Device level operations mainly involve 76 device power management operations and commands to Interconnect 77 layers. Device level configurations involve handling of query 78 requests which are used to modify and retrieve configuration 79 information of the device. 80 812.2 UFS Transport Protocol (UTP) layer 82-------------------------------------- 83 84 The UTP layer provides services for 85 the higher layers through Service Access Points. UTP defines 3 86 service access points for higher layers. 87 88 * UDM_SAP: Device manager service access point is exposed to device 89 manager for device level operations. These device level operations 90 are done through query requests. 91 * UTP_CMD_SAP: Command service access point is exposed to UFS command 92 set layer (UCS) to transport commands. 93 * UTP_TM_SAP: Task management service access point is exposed to task 94 manager to transport task management functions. 95 96 UTP transports messages through UFS protocol information unit (UPIU). 97 982.3 UFS Interconnect (UIC) Layer 99-------------------------------- 100 101 UIC is the lowest layer of the UFS layered architecture. It handles 102 the connection between UFS host and UFS device. UIC consists of 103 MIPI UniPro and MIPI M-PHY. UIC provides 2 service access points 104 to upper layer: 105 106 * UIC_SAP: To transport UPIU between UFS host and UFS device. 107 * UIO_SAP: To issue commands to Unipro layers. 108 109 1103. UFSHCD Overview 111================== 112 113The UFS host controller driver is based on the Linux SCSI Framework. 114UFSHCD is a low-level device driver which acts as an interface between 115the SCSI Midlayer and PCIe-based UFS host controllers. 116 117The current UFSHCD implementation supports the following functionality: 118 1193.1 UFS controller initialization 120--------------------------------- 121 122 The initialization module brings the UFS host controller to active state 123 and prepares the controller to transfer commands/responses between 124 UFSHCD and UFS device. 125 1263.2 UTP Transfer requests 127------------------------- 128 129 Transfer request handling module of UFSHCD receives SCSI commands 130 from the SCSI Midlayer, forms UPIUs and issues the UPIUs to the UFS Host 131 controller. Also, the module decodes responses received from the UFS 132 host controller in the form of UPIUs and intimates the SCSI Midlayer 133 of the status of the command. 134 1353.3 UFS error handling 136---------------------- 137 138 Error handling module handles Host controller fatal errors, 139 Device fatal errors and UIC interconnect layer-related errors. 140 1413.4 SCSI Error handling 142----------------------- 143 144 This is done through UFSHCD SCSI error handling routines registered 145 with the SCSI Midlayer. Examples of some of the error handling commands 146 issues by the SCSI Midlayer are Abort task, LUN reset and host reset. 147 UFSHCD Routines to perform these tasks are registered with 148 SCSI Midlayer through .eh_abort_handler, .eh_device_reset_handler and 149 .eh_host_reset_handler. 150 151In this version of UFSHCD, Query requests and power management 152functionality are not implemented. 153 1544. BSG Support 155============== 156 157This transport driver supports exchanging UFS protocol information units 158(UPIUs) with a UFS device. Typically, user space will allocate 159struct ufs_bsg_request and struct ufs_bsg_reply (see ufs_bsg.h) as 160request_upiu and reply_upiu respectively. Filling those UPIUs should 161be done in accordance with JEDEC spec UFS2.1 paragraph 10.7. 162*Caveat emptor*: The driver makes no further input validations and sends the 163UPIU to the device as it is. Open the bsg device in /dev/ufs-bsg and 164send SG_IO with the applicable sg_io_v4:: 165 166 io_hdr_v4.guard = 'Q'; 167 io_hdr_v4.protocol = BSG_PROTOCOL_SCSI; 168 io_hdr_v4.subprotocol = BSG_SUB_PROTOCOL_SCSI_TRANSPORT; 169 io_hdr_v4.response = (__u64)reply_upiu; 170 io_hdr_v4.max_response_len = reply_len; 171 io_hdr_v4.request_len = request_len; 172 io_hdr_v4.request = (__u64)request_upiu; 173 if (dir == SG_DXFER_TO_DEV) { 174 io_hdr_v4.dout_xfer_len = (uint32_t)byte_cnt; 175 io_hdr_v4.dout_xferp = (uintptr_t)(__u64)buff; 176 } else { 177 io_hdr_v4.din_xfer_len = (uint32_t)byte_cnt; 178 io_hdr_v4.din_xferp = (uintptr_t)(__u64)buff; 179 } 180 181If you wish to read or write a descriptor, use the appropriate xferp of 182sg_io_v4. 183 184The userspace tool that interacts with the ufs-bsg endpoint and uses its 185UPIU-based protocol is available at: 186 187 https://github.com/westerndigitalcorporation/ufs-tool 188 189For more detailed information about the tool and its supported 190features, please see the tool's README. 191 192UFS specifications can be found at: 193 194- UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf 195- UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf