scsi: docs: convert ufs.txt to ReST

Link: https://lore.kernel.org/r/052d45576e342a217185e91a83793b384b1592a4.1583136624.git.mchehab+huawei@kernel.org
Acked-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 195 insertions, 0 deletions

diff --git a/Documentation/scsi/ufs.rst b/Documentation/scsi/ufs.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+=======================
+Universal Flash Storage
+=======================
+
+
+.. Contents
+
+   1. Overview
+   2. UFS Architecture Overview
+     2.1 Application Layer
+     2.2 UFS Transport Protocol(UTP) layer
+     2.3 UFS Interconnect(UIC) Layer
+   3. UFSHCD Overview
+     3.1 UFS controller initialization
+     3.2 UTP Transfer requests
+     3.3 UFS error handling
+     3.4 SCSI Error handling
+
+
+1. Overview
+===========
+
+Universal Flash Storage(UFS) is a storage specification for flash devices.
+It is aimed to provide a universal storage interface for both
+embedded and removable flash memory based storage in mobile
+devices such as smart phones and tablet computers. The specification
+is defined by JEDEC Solid State Technology Association. UFS is based
+on MIPI M-PHY physical layer standard. UFS uses MIPI M-PHY as the
+physical layer and MIPI Unipro as the link layer.
+
+The main goals of UFS is to provide:
+
+ * Optimized performance:
+
+   For UFS version 1.0 and 1.1 the target performance is as follows:
+
+   - Support for Gear1 is mandatory (rate A: 1248Mbps, rate B: 1457.6Mbps)
+   - Support for Gear2 is optional (rate A: 2496Mbps, rate B: 2915.2Mbps)
+
+   Future version of the standard,
+
+   - Gear3 (rate A: 4992Mbps, rate B: 5830.4Mbps)
+
+ * Low power consumption
+ * High random IOPs and low latency
+
+
+2. UFS Architecture Overview
+============================
+
+UFS has a layered communication architecture which is based on SCSI
+SAM-5 architectural model.
+
+UFS communication architecture consists of following layers,
+
+2.1 Application Layer
+---------------------
+
+  The Application layer is composed of UFS command set layer(UCS),
+  Task Manager and Device manager. The UFS interface is designed to be
+  protocol agnostic, however SCSI has been selected as a baseline
+  protocol for versions 1.0 and 1.1 of UFS protocol  layer.
+
+  UFS supports subset of SCSI commands defined by SPC-4 and SBC-3.
+
+  * UCS:
+     It handles SCSI commands supported by UFS specification.
+  * Task manager:
+     It handles task management functions defined by the
+     UFS which are meant for command queue control.
+  * Device manager:
+     It handles device level operations and device
+     configuration operations. Device level operations mainly involve
+     device power management operations and commands to Interconnect
+     layers. Device level configurations involve handling of query
+     requests which are used to modify and retrieve configuration
+     information of the device.
+
+2.2 UFS Transport Protocol(UTP) layer
+-------------------------------------
+
+  UTP layer provides services for
+  the higher layers through Service Access Points. UTP defines 3
+  service access points for higher layers.
+
+  * UDM_SAP: Device manager service access point is exposed to device
+    manager for device level operations. These device level operations
+    are done through query requests.
+  * UTP_CMD_SAP: Command service access point is exposed to UFS command
+    set layer(UCS) to transport commands.
+  * UTP_TM_SAP: Task management service access point is exposed to task
+    manager to transport task management functions.
+
+  UTP transports messages through UFS protocol information unit(UPIU).
+
+2.3 UFS Interconnect(UIC) Layer
+-------------------------------
+
+  UIC is the lowest layer of UFS layered architecture. It handles
+  connection between UFS host and UFS device. UIC consists of
+  MIPI UniPro and MIPI M-PHY. UIC provides 2 service access points
+  to upper layer,
+
+  * UIC_SAP: To transport UPIU between UFS host and UFS device.
+  * UIO_SAP: To issue commands to Unipro layers.
+
+
+3. UFSHCD Overview
+==================
+
+The UFS host controller driver is based on Linux SCSI Framework.
+UFSHCD is a low level device driver which acts as an interface between
+SCSI Midlayer and PCIe based UFS host controllers.
+
+The current UFSHCD implementation supports following functionality,
+
+3.1 UFS controller initialization
+---------------------------------
+
+  The initialization module brings UFS host controller to active state
+  and prepares the controller to transfer commands/response between
+  UFSHCD and UFS device.
+
+3.2 UTP Transfer requests
+-------------------------
+
+  Transfer request handling module of UFSHCD receives SCSI commands
+  from SCSI Midlayer, forms UPIUs and issues the UPIUs to UFS Host
+  controller. Also, the module decodes, responses received from UFS
+  host controller in the form of UPIUs and intimates the SCSI Midlayer
+  of the status of the command.
+
+3.3 UFS error handling
+----------------------
+
+  Error handling module handles Host controller fatal errors,
+  Device fatal errors and UIC interconnect layer related errors.
+
+3.4 SCSI Error handling
+-----------------------
+
+  This is done through UFSHCD SCSI error handling routines registered
+  with SCSI Midlayer. Examples of some of the error handling commands
+  issues by SCSI Midlayer are Abort task, Lun reset and host reset.
+  UFSHCD Routines to perform these tasks are registered with
+  SCSI Midlayer through .eh_abort_handler, .eh_device_reset_handler and
+  .eh_host_reset_handler.
+
+In this version of UFSHCD Query requests and power management
+functionality are not implemented.
+
+4. BSG Support
+==============
+
+This transport driver supports exchanging UFS protocol information units
+(UPIUs) with a UFS device. Typically, user space will allocate
+struct ufs_bsg_request and struct ufs_bsg_reply (see ufs_bsg.h) as
+request_upiu and reply_upiu respectively.  Filling those UPIUs should
+be done in accordance with JEDEC spec UFS2.1 paragraph 10.7.
+*Caveat emptor*: The driver makes no further input validations and sends the
+UPIU to the device as it is.  Open the bsg device in /dev/ufs-bsg and
+send SG_IO with the applicable sg_io_v4::
+
+	io_hdr_v4.guard = 'Q';
+	io_hdr_v4.protocol = BSG_PROTOCOL_SCSI;
+	io_hdr_v4.subprotocol = BSG_SUB_PROTOCOL_SCSI_TRANSPORT;
+	io_hdr_v4.response = (__u64)reply_upiu;
+	io_hdr_v4.max_response_len = reply_len;
+	io_hdr_v4.request_len = request_len;
+	io_hdr_v4.request = (__u64)request_upiu;
+	if (dir == SG_DXFER_TO_DEV) {
+		io_hdr_v4.dout_xfer_len = (uint32_t)byte_cnt;
+		io_hdr_v4.dout_xferp = (uintptr_t)(__u64)buff;
+	} else {
+		io_hdr_v4.din_xfer_len = (uint32_t)byte_cnt;
+		io_hdr_v4.din_xferp = (uintptr_t)(__u64)buff;
+	}
+
+If you wish to read or write a descriptor, use the appropriate xferp of
+sg_io_v4.
+
+The userspace tool that interacts with the ufs-bsg endpoint and uses its
+upiu-based protocol is available at:
+
+	https://github.com/westerndigitalcorporation/ufs-tool
+
+For more detailed information about the tool and its supported
+features, please see the tool's README.
+
+UFS Specifications can be found at:
+
+- UFS - http://www.jedec.org/sites/default/files/docs/JESD220.pdf
+- UFSHCI - http://www.jedec.org/sites/default/files/docs/JESD223.pdf