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195 lines
6.6 KiB
195 lines
6.6 KiB
.. 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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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 is aimed 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 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 is 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 following layers, |
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2.1 Application Layer |
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--------------------- |
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The Application layer is composed of 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 UFS protocol layer. |
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UFS supports 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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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 UFS layered architecture. It handles |
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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 Linux SCSI Framework. |
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UFSHCD is a low level device driver which acts as an interface between |
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SCSI Midlayer and PCIe based UFS host controllers. |
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The current UFSHCD implementation supports following functionality, |
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3.1 UFS controller initialization |
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--------------------------------- |
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The initialization module brings UFS host controller to active state |
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and prepares the controller to transfer commands/response 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 SCSI Midlayer, forms UPIUs and issues the UPIUs to UFS Host |
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controller. Also, the module decodes, responses received from 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 SCSI Midlayer. Examples of some of the error handling commands |
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issues by 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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