1 .. SPDX-License-Identifier: GPL-2.0
2
3 =======================
4 Universal 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
24 1. Overview
25 ===========
26
27 Universal Flash Storage (UFS) is a storage specification for flash devices.
28 It aims to provide a universal storage interface for both
29 embedded and removable flash memory-based storage in mobile
30 devices such as smart phones and tablet computers. The specification
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
33 physical layer and MIPI Unipro as the link layer.
34
35 The 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
52 2. UFS Architecture Overview
53 ============================
54
55 UFS has a layered communication architecture which is based on SCSI
56 SAM-5 architectural model.
57
58 UFS communication architecture consists of the following layers.
59
60 2.1 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
83 2.2 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
100 2.3 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
112 3. UFSHCD Overview
113 ==================
114
115 The UFS host controller driver is based on the Linux SCSI Framework.
116 UFSHCD is a low-level device driver which acts as an interface between
117 the SCSI Midlayer and PCIe-based UFS host controllers.
118
119 The current UFSHCD implementation supports the following functionality:
120
121 3.1 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
128 3.2 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
137 3.3 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
143 3.4 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
153 In this version of UFSHCD, Query requests and power management
154 functionality are not implemented.
155
156 4. BSG Support
157 ==============
158
159 This transport driver supports exchanging UFS protocol information units
160 (UPIUs) with a UFS device. Typically, user space will allocate
161 struct ufs_bsg_request and struct ufs_bsg_reply (see ufs_bsg.h) as
162 request_upiu and reply_upiu respectively. Filling those UPIUs should
163 be done in accordance with JEDEC spec UFS2.1 paragraph 10.7.
164 *Caveat emptor*: The driver makes no further input validations and sends the
165 UPIU to the device as it is. Open the bsg device in /dev/ufs-bsg and
166 send 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
183 If you wish to read or write a descriptor, use the appropriate xferp of
184 sg_io_v4.
185
186 The userspace tool that interacts with the ufs-bsg endpoint and uses its
187 UPIU-based protocol is available at:
188
189 https://github.com/westerndigitalcorporation/ufs-tool
190
191 For more detailed information about the tool and its supported
192 features, please see the tool's README.
193
194 UFS 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
199 5. UFS Reference Clock Frequency configuration
200 ==============================================
201
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
204 parts. ACPI-based system can specify the frequency using ACPI
205 Device-Specific Data property named "ref-clk-freq". In both ways the value
206 is interpreted as frequency in Hz and must match one of the values given in
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
210 set accordingly and will modify it if there is a mismatch.
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.