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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
- 4. BSG Support
- 5. UFS Reference Clock Frequency configuration
- 1. Overview
- ===========
- Universal Flash Storage (UFS) is a storage specification for flash devices.
- It aims 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 the 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 are 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 the following layers.
- 2.1 Application Layer
- ---------------------
- The Application layer is composed of the 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 the UFS protocol layer.
- UFS supports a 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
- --------------------------------------
- The 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 the UFS layered architecture. It handles
- the 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 the Linux SCSI Framework.
- UFSHCD is a low-level device driver which acts as an interface between
- the SCSI Midlayer and PCIe-based UFS host controllers.
- The current UFSHCD implementation supports the following functionality:
- 3.1 UFS controller initialization
- ---------------------------------
- The initialization module brings the UFS host controller to active state
- and prepares the controller to transfer commands/responses between
- UFSHCD and UFS device.
- 3.2 UTP Transfer requests
- -------------------------
- Transfer request handling module of UFSHCD receives SCSI commands
- from the SCSI Midlayer, forms UPIUs and issues the UPIUs to the UFS Host
- controller. Also, the module decodes responses received from the 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 the SCSI Midlayer. Examples of some of the error handling commands
- issues by the 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
- 5. UFS Reference Clock Frequency configuration
- ==============================================
- Devicetree can define a clock named "ref_clk" under the UFS controller node
- to specify the intended reference clock frequency for the UFS storage
- parts. ACPI-based system can specify the frequency using ACPI
- Device-Specific Data property named "ref-clk-freq". In both ways the value
- is interpreted as frequency in Hz and must match one of the values given in
- the UFS specification. UFS subsystem will attempt to read the value when
- executing common controller initialization. If the value is available, UFS
- subsytem will ensure the bRefClkFreq attribute of the UFS storage device is
- set accordingly and will modify it if there is a mismatch.
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