[PATCH v3 5/5] Documentation: UFS Host Controller Driver

[Santosh Y <santoshsy@gmail.com>]

From: Santosh Yaraganavi <santoshsy@gmail.com>

The document provides Universal Flash Storage(UFS) and
UFS host controller driver overview.

Signed-off-by: Santosh Yaraganavi <santoshsy@gmail.com>
Reviewed-by: Vishak G <vishak.g@samsung.com>
Reviewed-by: Namjae Jeon <linkinjeon@gmail.com>
---
 Documentation/scsi/00-INDEX |    2 +
 Documentation/scsi/ufs.txt  |  133 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 135 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/scsi/ufs.txt

diff --git a/Documentation/scsi/00-INDEX b/Documentation/scsi/00-INDEX
index b48ded5..b7dd650 100644
--- a/Documentation/scsi/00-INDEX
+++ b/Documentation/scsi/00-INDEX
@@ -94,3 +94,5 @@ sym53c8xx_2.txt
 	- info on second generation driver for sym53c8xx based adapters
 tmscsim.txt
 	- info on driver for AM53c974 based adapters
+ufs.txt
+	- info on Universal Flash Storage(UFS) and UFS host controller driver.
diff --git a/Documentation/scsi/ufs.txt b/Documentation/scsi/ufs.txt
new file mode 100644
index 0000000..41a6164
--- /dev/null
+++ b/Documentation/scsi/ufs.txt
@@ -0,0 +1,133 @@
+                       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.
+
+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
-- 
1.7.5.4