MTD overview

SUMMARY
The MTD (Memory Technology Device) subsystem provides an abstraction layer for raw Flash memories. It makes it possible to use the same API when working with different Flash types and technologies, e.g. SLC NAND, SPI NOR, ...

1 Framework purpose

The purpose of this article is to introduce the MTD Linux subsystem:

  • General information
  • Main components/stakeholders
  • How to use the MTD API

2 System overview

2.1 For ecosystem release ≥ v1.1.0 More info.png

MTD v1.1.0.png

2.2 For ecosystem release v1.0.0 More info.png

Mtd.png

2.3 Component description

  • User space applications that perform file I/O need to view the Flash memory as if it was a disk, whereas programs that wish to accomplish raw I/O access the memory as if it was a character device.
  • VFS (Kernel space)

Virtual File System. Please refer to the VFS documentation [1].

  • mtdchar (Kernel space)

Usually referred to as /dev/mtdX. For MTD character devices, please refer to the MTD overview documentation [2].

  • mtdblock (Kernel space)

Usually referred to as /dev/mtdblockX. Do not use mtdblock unless you know exactly what you are doing. For MTD block devices, please refer to the MTD block documentation [3].

  • JFFS2 (Kernel space)

Journally Flash File System. Please refer to the MTD JFFS2 documentation [4].

  • UBI (Kernel space)

Unsorted Block Images. Please refer to the MTD UBI documentation [5].

  • UBIFS (Kernel space)

UBI File System. Please refer to the MTD UBIFS documentation [6].

  • MTD core (Kernel space)

The MTD core provides an abstraction layer for raw Flash memories.

  • Raw NAND subsystem (Kernel space)

The Raw NAND protocol is used in the MTD subsystem for interfacing NAND Flash memories.

  • SPI-MEM subsystem (Kernel space)

The SPI-MEM protocol is used in the MTD subsystem for interfacing all kinds of SPI memories (NORs, NANDs)

  • SPI-NAND subsystem (Kernel space)

The SPI-NAND protocol is used in the MTD subsystem for interfacing SPI NAND Flash memories.

  • SPI-NOR subsystem (Kernel space)

The SPI-NOR protocol is used in the MTD subsystem for interfacing SPI NOR Flash memories.

  • FMC driver (Kernel space) / FMC (Hardware)

Please refer to the FMC internal peripheral.

  • QUADSPI driver (Kernel space) / QUADSPI (Hardware)

Please refer to the QUADSPI internal peripheral.

2.4 API description

For the Linux MTD API description, please refer to the MTD API documentation [7].

3 Configuration

3.1 Kernel configuration

MTD is activated by default in ST deliveries. Nevertheless, if a specific configuration is needed, this section indicates how MTD can be activated/deactivated in the kernel.

Activate MTD in the kernel configuration with the Linux Menuconfig tool: Menuconfig or how to configure kernel.

3.1.1 SLC NAND Flash memory

[*] Device Drivers --->
    <*> Memory Technology Device (MTD) support --->
        <*> RAW/Parallel NAND Device Support --->
            <*> Support for NAND controller on STM32MP Socs.

3.1.2 SPI NOR/NAND Flash memory

[*] Device Drivers --->
    <*> Memory Technology Device (MTD) support --->
        Self-contained MTD device drivers --->
            <*> Support most SPI Flash chips (AT26DF, M25P, W25X, ...)      
        <*> SPI NAND device Support
        <*> SPI-NOR device support
    <*> SPI support --->
        -*- SPI memory extension
        <*> STMicroelectronics STM32 QUAD SPI controller

3.2 Device tree configuration

The DT configuration can be done thanks to STM32CubeMX.

3.2.1 NAND Flash memory

Please refer to the FMC device tree configuration.

3.2.2 SPI NOR/NAND Flash memory

Please refer to the QUADSPI device tree configuration.

4 How to use the framework

A file system, which handles read/write/erase operations, can be used over the MTD Framework. Please refer to the UBIFS support through MTD.

You can also interact with the MTD subsystem using the MTD utilities. The MTD utilities[8] are a set of tools that can be used to perform operations on Flash memories through the MTD character interface.

The most common utilities used are:

  • mtdinfo
  • flash_erase
  • flashcp
  • nandwrite
  • nanddump
 root:~# mtdinfo -a
 Count of MTD devices:           9
 Present MTD devices:            mtd0, mtd1, mtd2, mtd3, mtd4, mtd5, mtd6, mtd7, mtd8
 Sysfs interface supported:      yes
mtd0 Name: fsbl Type: nand Eraseblock size: 262144 bytes, 256.0 KiB Amount of eraseblocks: 8 (2097152 bytes, 2.0 MiB) Minimum input/output unit size: 4096 bytes Sub-page size: 4096 bytes OOB size: 224 bytes Character device major/minor: 90:0 Bad blocks are allowed: true Device is writable: true
mtd1 Name: ssbl Type: nand Eraseblock size: 262144 bytes, 256.0 KiB Amount of eraseblocks: 8 (2097152 bytes, 2.0 MiB) Minimum input/output unit size: 4096 bytes Sub-page size: 4096 bytes OOB size: 224 bytes Character device major/minor: 90:2 Bad blocks are allowed: true Device is writable: true
mtd2 Name: UBI Type: nand Eraseblock size: 262144 bytes, 256.0 KiB Amount of eraseblocks: 4078 (1069023232 bytes, 1019.5 MiB) Minimum input/output unit size: 4096 bytes Sub-page size: 4096 bytes OOB size: 224 bytes Character device major/minor: 90:4 Bad blocks are allowed: true Device is writable: true
mtd3 Name: fsbl1 Type: nor Eraseblock size: 65536 bytes, 64.0 KiB Amount of eraseblocks: 4 (262144 bytes, 256.0 KiB) Minimum input/output unit size: 1 byte Sub-page size: 1 byte Character device major/minor: 90:6 Bad blocks are allowed: false Device is writable: true
mtd4 Name: fsbl2 Type: nor Eraseblock size: 65536 bytes, 64.0 KiB Amount of eraseblocks: 4 (262144 bytes, 256.0 KiB) Minimum input/output unit size: 1 byte Sub-page size: 1 byte Character device major/minor: 90:8 Bad blocks are allowed: false Device is writable: true
mtd5 Name: ssbl Type: nor Eraseblock size: 65536 bytes, 64.0 KiB Amount of eraseblocks: 32 (2097152 bytes, 2.0 MiB) Minimum input/output unit size: 1 byte Sub-page size: 1 byte Character device major/minor: 90:10 Bad blocks are allowed: false Device is writable: true
mtd6 Name: logo Type: nor Eraseblock size: 65536 bytes, 64.0 KiB Amount of eraseblocks: 4 (262144 bytes, 256.0 KiB) Minimum input/output unit size: 1 byte Sub-page size: 1 byte Character device major/minor: 90:12 Bad blocks are allowed: false Device is writable: true
mtd7 Name: nor_user Type: nor Eraseblock size: 65536 bytes, 64.0 KiB Amount of eraseblocks: 980 (64225280 bytes, 61.2 MiB) Minimum input/output unit size: 1 byte Sub-page size: 1 byte Character device major/minor: 90:14 Bad blocks are allowed: false Device is writable: true
mtd8 Name: 58003000.qspi Type: nor Eraseblock size: 65536 bytes, 64.0 KiB Amount of eraseblocks: 1024 (67108864 bytes, 64.0 MiB) Minimum input/output unit size: 1 byte Sub-page size: 1 byte Character device major/minor: 90:16 Bad blocks are allowed: false Device is writable: true

5 How to trace and debug the framework

5.1 How to monitor

The sysfs interface provides detail information on each mtd device.

 root:~# cat /sys/class/mtd/mtd0/name
 fsbl
 root:~# cat /sys/class/mtd/mtd0/type
 nand
 root:~# cat /sys/class/mtd/mtd0/erasesize
 262144
 root:~# cat /sys/class/mtd/mtd0/ecc_strength
 8
 root:~# cat /sys/class/mtd/mtd0/bad_blocks
 0
 root:~# cat /sys/class/mtd/mtd0/ecc_failures
 0

5.2 How to trace

A detail dynamic trace is available here How to use the kernel dynamic debug.

 root:~# echo "file drivers/mtd/* +p" > /sys/kernel/debug/dynamic_debug/control

6 Source code location

The MTD framework is here .

7 To go further

Please refer to the MTD FAQs documentation [9].

8 References

Please refer to the following links for full description:



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