1 Universal Flash Storage 2 ======================= 3 4 5Contents 6-------- 7 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 18 19 201. Overview 21----------- 22 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. 30 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 40 41 422. UFS Architecture Overview 43---------------------------- 44 45UFS has a layered communication architecture which is based on SCSI 46SAM-5 architectural model. 47 48UFS communication architecture consists of following layers, 49 502.1 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. 66 672.2 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). 80 812.3 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 90 913. UFSHCD Overview 92------------------ 93 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. 97 98The current UFSHCD implementation supports following functionality, 99 1003.1 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 1063.2 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 1143.3 UFS error handling 115 116 Error handling module handles Host controller fatal errors, 117 Device fatal errors and UIC interconnect layer related errors. 118 1193.4 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 128In this version of UFSHCD Query requests and power management 129functionality are not implemented. 130 1314. BSG Support 132------------------ 133 134This transport driver supports exchanging UFS protocol information units 135(UPIUs) with a UFS device. Typically, user space will allocate 136struct ufs_bsg_request and struct ufs_bsg_reply (see ufs_bsg.h) as 137request_upiu and reply_upiu respectively. Filling those UPIUs should 138be done in accordance with JEDEC spec UFS2.1 paragraph 10.7. 139*Caveat emptor*: The driver makes no further input validations and sends the 140UPIU to the device as it is. Open the bsg device in /dev/ufs-bsg and 141send SG_IO with the applicable sg_io_v4: 142 143 io_hdr_v4.guard = 'Q'; 144 io_hdr_v4.protocol = BSG_PROTOCOL_SCSI; 145 io_hdr_v4.subprotocol = BSG_SUB_PROTOCOL_SCSI_TRANSPORT; 146 io_hdr_v4.response = (__u64)reply_upiu; 147 io_hdr_v4.max_response_len = reply_len; 148 io_hdr_v4.request_len = request_len; 149 io_hdr_v4.request = (__u64)request_upiu; 150 if (dir == SG_DXFER_TO_DEV) { 151 io_hdr_v4.dout_xfer_len = (uint32_t)byte_cnt; 152 io_hdr_v4.dout_xferp = (uintptr_t)(__u64)buff; 153 } else { 154 io_hdr_v4.din_xfer_len = (uint32_t)byte_cnt; 155 io_hdr_v4.din_xferp = (uintptr_t)(__u64)buff; 156 } 157 158If you wish to read or write a descriptor, use the appropriate xferp of 159sg_io_v4. 160 161The userspace tool that interacts with the ufs-bsg endpoint and uses its 162upiu-based protocol is available at: 163 164 https://github.com/westerndigitalcorporation/ufs-tool 165 166For more detailed information about the tool and its supported 167features, please see the tool's README. 168 169UFS Specifications can be found at, 170UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf 171UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf 172
