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Documentation / scsi / ufs.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

1	                       Universal Flash Storage
2	                       =======================
3	
4	
5	Contents
6	--------
7	
8	1. Overview
9	2. UFS Architecture Overview
10	  2.1 Application Layer
11	  2.2 UFS Transport Protocol(UTP) layer
12	  2.3 UFS Interconnect(UIC) Layer
13	3. 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	
20	1. Overview
21	-----------
22	
23	Universal Flash Storage(UFS) is a storage specification for flash devices.
24	It is aimed to provide a universal storage interface for both
25	embedded and removable flash memory based storage in mobile
26	devices such as smart phones and tablet computers. The specification
27	is defined by JEDEC Solid State Technology Association. UFS is based
28	on MIPI M-PHY physical layer standard. UFS uses MIPI M-PHY as the
29	physical layer and MIPI Unipro as the link layer.
30	
31	The 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	
42	2. UFS Architecture Overview
43	----------------------------
44	
45	UFS has a layered communication architecture which is based on SCSI
46	SAM-5 architectural model.
47	
48	UFS communication architecture consists of following layers,
49	
50	2.1 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	
67	2.2 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	
81	2.3 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	
91	3. UFSHCD Overview
92	------------------
93	
94	The UFS host controller driver is based on Linux SCSI Framework.
95	UFSHCD is a low level device driver which acts as an interface between
96	SCSI Midlayer and PCIe based UFS host controllers.
97	
98	The current UFSHCD implementation supports following functionality,
99	
100	3.1 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	
106	3.2 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	
114	3.3 UFS error handling
115	
116	  Error handling module handles Host controller fatal errors,
117	  Device fatal errors and UIC interconnect layer related errors.
118	
119	3.4 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	
128	In this version of UFSHCD Query requests and power management
129	functionality are not implemented.
130	
131	UFS Specifications can be found at,
132	UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf
133	UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf
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