| 1 | ============================================== |
| 2 | Embedded device command line partition parsing |
| 3 | ============================================== |
| 4 | |
| 5 | The "blkdevparts" command line option adds support for reading the |
| 6 | block device partition table from the kernel command line. |
| 7 | |
| 8 | It is typically used for fixed block (eMMC) embedded devices. |
| 9 | It has no MBR, so saves storage space. Bootloader can be easily accessed |
| 10 | by absolute address of data on the block device. |
| 11 | Users can easily change the partition. |
| 12 | |
| 13 | The format for the command line is just like mtdparts: |
| 14 | |
| 15 | blkdevparts=<blkdev-def>[;<blkdev-def>] |
| 16 | <blkdev-def> := <blkdev-id>:<partdef>[,<partdef>] |
| 17 | <partdef> := <size>[@<offset>](part-name) |
| 18 | |
| 19 | <blkdev-id> |
| 20 | block device disk name. Embedded device uses fixed block device. |
| 21 | Its disk name is also fixed, such as: mmcblk0, mmcblk1, mmcblk0boot0. |
| 22 | |
| 23 | <size> |
| 24 | partition size, in bytes, such as: 512, 1m, 1G. |
| 25 | size may contain an optional suffix of (upper or lower case): |
| 26 | |
| 27 | K, M, G, T, P, E. |
| 28 | |
| 29 | "-" is used to denote all remaining space. |
| 30 | |
| 31 | <offset> |
| 32 | partition start address, in bytes. |
| 33 | offset may contain an optional suffix of (upper or lower case): |
| 34 | |
| 35 | K, M, G, T, P, E. |
| 36 | |
| 37 | (part-name) |
| 38 | partition name. Kernel sends uevent with "PARTNAME". Application can |
| 39 | create a link to block device partition with the name "PARTNAME". |
| 40 | User space application can access partition by partition name. |
| 41 | |
| 42 | Example: |
| 43 | |
| 44 | eMMC disk names are "mmcblk0" and "mmcblk0boot0". |
| 45 | |
| 46 | bootargs:: |
| 47 | |
| 48 | 'blkdevparts=mmcblk0:1G(data0),1G(data1),-;mmcblk0boot0:1m(boot),-(kernel)' |
| 49 | |
| 50 | dmesg:: |
| 51 | |
| 52 | mmcblk0: p1(data0) p2(data1) p3() |
| 53 | mmcblk0boot0: p1(boot) p2(kernel) |