0001 .. SPDX-License-Identifier: GPL-2.0
0002
0003 =======================
0004 Universal Flash Storage
0005 =======================
0006
0007
0008 .. Contents
0009
0010 1. Overview
0011 2. UFS Architecture Overview
0012 2.1 Application Layer
0013 2.2 UFS Transport Protocol (UTP) layer
0014 2.3 UFS Interconnect (UIC) Layer
0015 3. UFSHCD Overview
0016 3.1 UFS controller initialization
0017 3.2 UTP Transfer requests
0018 3.3 UFS error handling
0019 3.4 SCSI Error handling
0020 4. BSG Support
0021 5. UFS Reference Clock Frequency configuration
0022
0023
0024 1. Overview
0025 ===========
0026
0027 Universal Flash Storage (UFS) is a storage specification for flash devices.
0028 It aims to provide a universal storage interface for both
0029 embedded and removable flash memory-based storage in mobile
0030 devices such as smart phones and tablet computers. The specification
0031 is defined by JEDEC Solid State Technology Association. UFS is based
0032 on the MIPI M-PHY physical layer standard. UFS uses MIPI M-PHY as the
0033 physical layer and MIPI Unipro as the link layer.
0034
0035 The main goals of UFS are to provide:
0036
0037 * Optimized performance:
0038
0039 For UFS version 1.0 and 1.1 the target performance is as follows:
0040
0041 - Support for Gear1 is mandatory (rate A: 1248Mbps, rate B: 1457.6Mbps)
0042 - Support for Gear2 is optional (rate A: 2496Mbps, rate B: 2915.2Mbps)
0043
0044 Future version of the standard,
0045
0046 - Gear3 (rate A: 4992Mbps, rate B: 5830.4Mbps)
0047
0048 * Low power consumption
0049 * High random IOPs and low latency
0050
0051
0052 2. UFS Architecture Overview
0053 ============================
0054
0055 UFS has a layered communication architecture which is based on SCSI
0056 SAM-5 architectural model.
0057
0058 UFS communication architecture consists of the following layers.
0059
0060 2.1 Application Layer
0061 ---------------------
0062
0063 The Application layer is composed of the UFS command set layer (UCS),
0064 Task Manager and Device manager. The UFS interface is designed to be
0065 protocol agnostic, however SCSI has been selected as a baseline
0066 protocol for versions 1.0 and 1.1 of the UFS protocol layer.
0067
0068 UFS supports a subset of SCSI commands defined by SPC-4 and SBC-3.
0069
0070 * UCS:
0071 It handles SCSI commands supported by UFS specification.
0072 * Task manager:
0073 It handles task management functions defined by the
0074 UFS which are meant for command queue control.
0075 * Device manager:
0076 It handles device level operations and device
0077 configuration operations. Device level operations mainly involve
0078 device power management operations and commands to Interconnect
0079 layers. Device level configurations involve handling of query
0080 requests which are used to modify and retrieve configuration
0081 information of the device.
0082
0083 2.2 UFS Transport Protocol (UTP) layer
0084 --------------------------------------
0085
0086 The UTP layer provides services for
0087 the higher layers through Service Access Points. UTP defines 3
0088 service access points for higher layers.
0089
0090 * UDM_SAP: Device manager service access point is exposed to device
0091 manager for device level operations. These device level operations
0092 are done through query requests.
0093 * UTP_CMD_SAP: Command service access point is exposed to UFS command
0094 set layer (UCS) to transport commands.
0095 * UTP_TM_SAP: Task management service access point is exposed to task
0096 manager to transport task management functions.
0097
0098 UTP transports messages through UFS protocol information unit (UPIU).
0099
0100 2.3 UFS Interconnect (UIC) Layer
0101 --------------------------------
0102
0103 UIC is the lowest layer of the UFS layered architecture. It handles
0104 the connection between UFS host and UFS device. UIC consists of
0105 MIPI UniPro and MIPI M-PHY. UIC provides 2 service access points
0106 to upper layer:
0107
0108 * UIC_SAP: To transport UPIU between UFS host and UFS device.
0109 * UIO_SAP: To issue commands to Unipro layers.
0110
0111
0112 3. UFSHCD Overview
0113 ==================
0114
0115 The UFS host controller driver is based on the Linux SCSI Framework.
0116 UFSHCD is a low-level device driver which acts as an interface between
0117 the SCSI Midlayer and PCIe-based UFS host controllers.
0118
0119 The current UFSHCD implementation supports the following functionality:
0120
0121 3.1 UFS controller initialization
0122 ---------------------------------
0123
0124 The initialization module brings the UFS host controller to active state
0125 and prepares the controller to transfer commands/responses between
0126 UFSHCD and UFS device.
0127
0128 3.2 UTP Transfer requests
0129 -------------------------
0130
0131 Transfer request handling module of UFSHCD receives SCSI commands
0132 from the SCSI Midlayer, forms UPIUs and issues the UPIUs to the UFS Host
0133 controller. Also, the module decodes responses received from the UFS
0134 host controller in the form of UPIUs and intimates the SCSI Midlayer
0135 of the status of the command.
0136
0137 3.3 UFS error handling
0138 ----------------------
0139
0140 Error handling module handles Host controller fatal errors,
0141 Device fatal errors and UIC interconnect layer-related errors.
0142
0143 3.4 SCSI Error handling
0144 -----------------------
0145
0146 This is done through UFSHCD SCSI error handling routines registered
0147 with the SCSI Midlayer. Examples of some of the error handling commands
0148 issues by the SCSI Midlayer are Abort task, LUN reset and host reset.
0149 UFSHCD Routines to perform these tasks are registered with
0150 SCSI Midlayer through .eh_abort_handler, .eh_device_reset_handler and
0151 .eh_host_reset_handler.
0152
0153 In this version of UFSHCD, Query requests and power management
0154 functionality are not implemented.
0155
0156 4. BSG Support
0157 ==============
0158
0159 This transport driver supports exchanging UFS protocol information units
0160 (UPIUs) with a UFS device. Typically, user space will allocate
0161 struct ufs_bsg_request and struct ufs_bsg_reply (see ufs_bsg.h) as
0162 request_upiu and reply_upiu respectively. Filling those UPIUs should
0163 be done in accordance with JEDEC spec UFS2.1 paragraph 10.7.
0164 *Caveat emptor*: The driver makes no further input validations and sends the
0165 UPIU to the device as it is. Open the bsg device in /dev/ufs-bsg and
0166 send SG_IO with the applicable sg_io_v4::
0167
0168 io_hdr_v4.guard = 'Q';
0169 io_hdr_v4.protocol = BSG_PROTOCOL_SCSI;
0170 io_hdr_v4.subprotocol = BSG_SUB_PROTOCOL_SCSI_TRANSPORT;
0171 io_hdr_v4.response = (__u64)reply_upiu;
0172 io_hdr_v4.max_response_len = reply_len;
0173 io_hdr_v4.request_len = request_len;
0174 io_hdr_v4.request = (__u64)request_upiu;
0175 if (dir == SG_DXFER_TO_DEV) {
0176 io_hdr_v4.dout_xfer_len = (uint32_t)byte_cnt;
0177 io_hdr_v4.dout_xferp = (uintptr_t)(__u64)buff;
0178 } else {
0179 io_hdr_v4.din_xfer_len = (uint32_t)byte_cnt;
0180 io_hdr_v4.din_xferp = (uintptr_t)(__u64)buff;
0181 }
0182
0183 If you wish to read or write a descriptor, use the appropriate xferp of
0184 sg_io_v4.
0185
0186 The userspace tool that interacts with the ufs-bsg endpoint and uses its
0187 UPIU-based protocol is available at:
0188
0189 https://github.com/westerndigitalcorporation/ufs-tool
0190
0191 For more detailed information about the tool and its supported
0192 features, please see the tool's README.
0193
0194 UFS specifications can be found at:
0195
0196 - UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf
0197 - UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf
0198
0199 5. UFS Reference Clock Frequency configuration
0200 ==============================================
0201
0202 Devicetree can define a clock named "ref_clk" under the UFS controller node
0203 to specify the intended reference clock frequency for the UFS storage
0204 parts. ACPI-based system can specify the frequency using ACPI
0205 Device-Specific Data property named "ref-clk-freq". In both ways the value
0206 is interpreted as frequency in Hz and must match one of the values given in
0207 the UFS specification. UFS subsystem will attempt to read the value when
0208 executing common controller initialization. If the value is available, UFS
0209 subsytem will ensure the bRefClkFreq attribute of the UFS storage device is
0210 set accordingly and will modify it if there is a mismatch.
