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'''SUMMARY '''<br>
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, ...

== 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

==System overview==
===For {{EcosystemRelease | revision=1.1.0 | range=and after}}===
[[File:MTD v1.1.0.png|center]]

<div class="mw-collapsible mw-collapsed">

===For {{EcosystemRelease | revision=1.0.0}}===
<div class="mw-collapsible-content">
[[File:mtd.png|center]]
</div></div>

===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 <ref>{{CodeSource | Linux kernel | Documentation/filesystems/vfs.txt | VFS}} </ref>.

* '''mtdchar''' (Kernel space)
Usually referred to as /dev/mtdX. For MTD character devices, please refer to the MTD overview documentation <ref>[http://www.linux-mtd.infradead.org/doc/general.html#L_overview MTD overview]</ref>.

* '''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 <ref>[http://www.linux-mtd.infradead.org/doc/general.html#L_mtdblock MTD block]</ref>.

* '''JFFS2''' (Kernel space)
Journally Flash File System. Please refer to the MTD JFFS2 documentation <ref>[http://www.linux-mtd.infradead.org/doc/jffs2.html MTD JFFS2]</ref>.

* '''UBI''' (Kernel space)
Unsorted Block Images. Please refer to the MTD UBI documentation <ref>[http://www.linux-mtd.infradead.org/doc/ubi.html MTD UBI]</ref>.

* '''UBIFS''' (Kernel space)
UBI File System. Please refer to the MTD UBIFS documentation <ref>[http://www.linux-mtd.infradead.org/doc/ubifs.html MTD UBIFS]</ref>.

* '''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]].

===API description===
For the Linux MTD API description, please refer to the MTD API documentation <ref>[http://www.linux-mtd.infradead.org/doc/general.html#L_mtd_api MTD API]</ref>.

==Configuration ==
===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]].

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

==== SPI NOR/NAND Flash memory ====
<pre>
[*] 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
</pre>

===Device tree configuration===
The DT configuration can be done thanks to [[STM32CubeMX]].

==== NAND Flash memory ====
Please refer to the [[FMC_device_tree_configuration| FMC device tree configuration]].

==== SPI NOR/NAND Flash memory ====
Please refer to the [[QUADSPI_device_tree_configuration| QUADSPI device tree configuration]].

== 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 [[How to support UBIFS through MTD|UBIFS support through MTD]].

You can also interact with the MTD subsystem using the MTD utilities.
The MTD utilities<ref>[http://www.linux-mtd.infradead.org MTD utils]</ref> 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<br>
  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<br>
  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<br>
  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<br>
  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<br>
  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<br>
  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<br>
  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<br>
  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<br>
  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

==How to trace and debug the framework==

===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

===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

==Source code location==
The MTD framework is {{CodeSource | Linux kernel | drivers/mtd  | here}}.

==To go further==
Please refer to the MTD FAQs documentation <ref>[http://www.linux-mtd.infradead.org/faq/general.html MTD FAQs]</ref>.

==References==
Please refer to the following links for full description:

<references />

<noinclude>
{{ArticleBasedOnModel | Framework overview article model}}
[[Category:Mass storage]]
</noinclude>