block: support embedded device command line partition

Read block device partition table from command line.  The partition used
for fixed block device (eMMC) embedded device.  It is no MBR, save
storage space.  Bootloader can be easily accessed by absolute address of
data on the block device.  Users can easily change the partition.

This code reference MTD partition, source "drivers/mtd/cmdlinepart.c"
About the partition verbose reference
"Documentation/block/cmdline-partition.txt"

[akpm@linux-foundation.org: fix printk text]
[yongjun_wei@trendmicro.com.cn: fix error return code in parse_parts()]
Signed-off-by: Cai Zhiyong <caizhiyong@huawei.com>
Cc: Karel Zak <kzak@redhat.com>
Cc: "Wanglin (Albert)" <albert.wanglin@huawei.com>
Cc: Marius Groeger <mag@sysgo.de>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Brian Norris <computersforpeace@gmail.com>
Cc: Artem Bityutskiy <dedekind@infradead.org>
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 39 insertions, 0 deletions

diff --git a/Documentation/block/cmdline-partition.txt b/Documentation/block/cmdline-partition.txt
new file mode 100644
index 000000000000..2bbf4cc40c3f
--- /dev/null
+++ b/Documentation/block/cmdline-partition.txt
@@ -0,0 +1,39 @@
+Embedded device command line partition
+=====================================================================
+
+Read block device partition table from command line.
+The partition used for fixed block device (eMMC) embedded device.
+It is no MBR, save storage space. Bootloader can be easily accessed
+by absolute address of data on the block device.
+Users can easily change the partition.
+
+The format for the command line is just like mtdparts:
+
+blkdevparts=<blkdev-def>[;<blkdev-def>]
+  <blkdev-def> := <blkdev-id>:<partdef>[,<partdef>]
+    <partdef> := <size>[@<offset>](part-name)
+
+<blkdev-id>
+    block device disk name, embedded device used fixed block device,
+    it's disk name also fixed. such as: mmcblk0, mmcblk1, mmcblk0boot0.
+
+<size>
+    partition size, in bytes, such as: 512, 1m, 1G.
+
+<offset>
+    partition start address, in bytes.
+
+(part-name)
+    partition name, kernel send uevent with "PARTNAME". application can create
+    a link to block device partition with the name "PARTNAME".
+    user space application can access partition by partition name.
+
+Example:
+    eMMC disk name is "mmcblk0" and "mmcblk0boot0"
+
+  bootargs:
+    'blkdevparts=mmcblk0:1G(data0),1G(data1),-;mmcblk0boot0:1m(boot),-(kernel)'
+
+  dmesg:
+    mmcblk0: p1(data0) p2(data1) p3()
+    mmcblk0boot0: p1(boot) p2(kernel)