MTD overview

Applicable for

STM32MP13x lines, STM32MP15x lines, STM32MP25x lines

The Linux^® 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, and so on.

1. Framework purpose[edit | edit source]

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[edit | edit source]

2.1. On STM32MP1 series[edit | edit source]

2.2. On STM32MP2 series[edit | edit source]

2.3. Component description[edit | edit source]

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.

CFI subsystem (Kernel space)

The Common Flash Interface protocol is used in the MTD subsystem for interfacing HYPERFLASH 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.

OCTOSPI driver (Kernel space) / OCTOSPI (Hardware)

Please refer to the OCTOSPI internal peripheral.

HyperBus driver (Kernel space) / OCTOSPI (Hardware)

Please refer to the OCTOSPI internal peripheral.

2.4. API description[edit | edit source]

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

3. Configuration[edit | edit source]

3.1. Kernel configuration[edit | edit source]

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[edit | edit source]

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

3.1.2. SPI NOR/NAND Flash memory[edit | edit source]

Device Drivers --->
    <*> Memory Technology Device (MTD) support ---> 
        NAND --->
            <*> SPI NAND device Support
        <*> SPI-NOR device support
    [*] SPI support --->
        -*- SPI memory extension
        <*> STMicroelectronics STM32 QUAD SPI controller
        <*> STMicroelectronics STM32 OCTO SPI controller

3.1.3. HYPERFLASH NOR Flash memory[edit | edit source]

Device Drivers --->
    <*> Memory Technology Device (MTD) support ---> 
        RAM/ROM/Flash chip drivers  --->
            -*- Detect flash chips by Common Flash Interface (CFI) probe
            -*- Support for CFI command set 0002 (AMD/Fujitsu/Spansion chips)
        <*> HyperBus support  --->
            --- HyperBus support
            <*> STM32 HyperBus driver

3.2. Device tree configuration[edit | edit source]

The DT configuration can be done thanks to STM32CubeMX.

3.2.1. NAND Flash memory[edit | edit source]

Please refer to the FMC device tree configuration.

3.2.2. SPI NOR/NAND Flash memory[edit | edit source]

4. How to use the framework[edit | edit source]

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[edit | edit source]

5.1. How to monitor[edit | edit source]

The sysfs interface provides detailed information for 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[edit | edit source]

A detailed 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[edit | edit source]

The MTD framework is here .

7. To go further[edit | edit source]

Please refer to the MTD FAQs documentation ^[9].

8. References[edit | edit source]

Please refer to the following links for full descriptions:

[1] VFS

[2] MTD overview

[3] MTD block

[4] MTD JFFS2

[5] MTD UBI

[6] MTD UBIFS

[7] MTD API

[8] MTD utils

[9] MTD FAQs

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]