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