How does Linux kernel create /dev/mtdx nodes?

Question

An example of the mtd partition table is in arch/arm/mach-omap2/board-omap3beagle.c for the beagleboard http://lxr.free-electrons.com/source/arch/arm/mach-omap2/board-omap3beagle.c

static struct mtd_partition omap3beagle_nand_partitions[] = {
/* All the partition sizes are listed in terms of NAND block size */
{
    .name       = "X-Loader",
    .offset     = 0,
    .size       = 4 * NAND_BLOCK_SIZE,
    .mask_flags = MTD_WRITEABLE,    /* force read-only */
},
{
    .name       = "U-Boot",
    .offset     = MTDPART_OFS_APPEND,   /* Offset = 0x80000 */
    .size       = 15 * NAND_BLOCK_SIZE,
    .mask_flags = MTD_WRITEABLE,    /* force read-only */
},
{
    .name       = "U-Boot Env",
    .offset     = MTDPART_OFS_APPEND,   /* Offset = 0x260000 */
    .size       = 1 * NAND_BLOCK_SIZE,
},
{
    .name       = "Kernel",
    .offset     = MTDPART_OFS_APPEND,   /* Offset = 0x280000 */
    .size       = 32 * NAND_BLOCK_SIZE,
},
{
    .name       = "File System",
    .offset     = MTDPART_OFS_APPEND,   /* Offset = 0x680000 */
    .size       = MTDPART_SIZ_FULL,
},
};

Another link states this: http://landley.net/kdocs/Documentation/DocBook/xhtml-nochunks/mtdnand.html In this link Nand flash driver board_init function passes the mtd_partition structure is passed to add_mtd_partitions(board_mtd, partition_info, NUM_PARTITIONS); function in file mtdcore.c file.

If I am right then does the mtdcores.c file create the mtd partitions?

Now I have two questions:

1> If I am right, then the omap3_beagle_init function in file /board-omap3beagle.c will call the omap_nand_flash_init function this will initialize the NAND & create /dev/mdtx nodes.

If I am not right then what creates the /dev/mtd0 nodes? Does the kernel create it or the NAND driver?

2> Also, is the omap3_beagle_init function the first function called by the kernel? Which file in the linux kernel is it called from?

Alexandre Belloni Alexandre Belloni · Accepted Answer · 2015-10-23T10:20:45

1/ There are multiples ways the device files can be created. Usually, they are now created using devtmpfs which is part of the kernel. When a driver or a subsystem registers a new device, devtmpfs_create_node is called This wakes up a thread that will add the device node to the devtmpfs filesystem.

If your kernel is not using devtmpfs, then you have to create those device files manually, using mknod. Also mdev is also a tool that can create device file. Finally, udev used to create device files but now relies on devtmpfs.

2/ omap3_beagle_init is definitively not the first function called by the kernel. After decompressing itself, the entry point is start_kernel in init/main.c. This is architecture independent. omap3_beagle_init is called from the customize_machine arch_initcall in arch/arm/kernel/setup.c

How does Linux kernel create /dev/mtdx nodes?

1 Answers