Kernel-4.18.0-80.el8_mtd-physmap

CFI or JEDEC memory-mapped NOR flash, MTD-RAM (NVRAM…)

Flash chips (Memory Technology Devices) are often used for solid state
file systems on embedded devices.

• compatible : should contain the specific model of mtd chip(s)
  used, if known, followed by either “cfi-flash”, “jedec-flash”,
  “mtd-ram” or “mtd-rom”.
• reg : Address range(s) of the mtd chip(s)
  It’s possible to (optionally) define multiple “reg” tuples so that
  non-identical chips can be described in one node.
• bank-width : Width (in bytes) of the bank. Equal to the
  device width times the number of interleaved chips.
• device-width : (optional) Width of a single mtd chip. If
  omitted, assumed to be equal to ‘bank-width’.
• #address-cells, #size-cells : Must be present if the device has
  sub-nodes representing partitions (see below). In this case
  both #address-cells and #size-cells must be equal to 1.
• no-unaligned-direct-access: boolean to disable the default direct
  mapping of the flash.
  On some platforms (e.g. MPC5200) a direct 1:1 mapping may cause
  problems with JFFS2 usage, as the local bus (LPB) doesn’t support
  unaligned accesses as implemented in the JFFS2 code via memcpy().
  By defining “no-unaligned-direct-access”, the flash will not be
  exposed directly to the MTD users (e.g. JFFS2) any more.
• linux,mtd-name: allow to specify the mtd name for retro capability with
  physmap-flash drivers as boot loader pass the mtd partition via the old
  device name physmap-flash.
• use-advanced-sector-protection: boolean to enable support for the
  advanced sector protection (Spansion: PPB - Persistent Protection
  Bits) locking.

For JEDEC compatible devices, the following additional properties
are defined:

• vendor-id : Contains the flash chip’s vendor id (1 byte).
• device-id : Contains the flash chip’s device id (1 byte).

For ROM compatible devices (and ROM fallback from cfi-flash), the following
additional (optional) property is defined:

• erase-size : The chip’s physical erase block size in bytes.

  The device tree may optionally contain endianness property.
  little-endian or big-endian : It Represents the endianness that should be used

                          by the controller to  properly read/write data
              from/to the flash. If this property is missing,
              the endianness is chosen by the system
              (potentially based on extra configuration options).
  

The device tree may optionally contain sub-nodes describing partitions of the
address space. See partition.txt for more detail.

Example:

flash@ff000000 {
    compatible = "amd,am29lv128ml", "cfi-flash";
    reg = <ff000000 01000000>;
    bank-width = <4>;
    device-width = <1>;
    #address-cells = <1>;
    #size-cells = <1>;
    fs@0 {
        label = "fs";
        reg = <0 f80000>;
    };
    firmware@f80000 {
        label ="firmware";
        reg = <f80000 80000>;
        read-only;
    };
};

Here an example with multiple “reg” tuples:

flash@f0000000,0 {
    #address-cells = <1>;
    #size-cells = <1>;
    compatible = "intel,PC48F4400P0VB", "cfi-flash";
    reg = <0 0x00000000 0x02000000
           0 0x02000000 0x02000000>;
    bank-width = <2>;
    partition@0 {
        label = "test-part1";
        reg = <0 0x04000000>;
    };
};

An example using SRAM:

sram@2,0 {
    compatible = "samsung,k6f1616u6a", "mtd-ram";
    reg = <2 0 0x00200000>;
    bank-width = <2>;
};