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authorRob Herring (Arm) <robh@kernel.org>2026-08-31 14:43:51 -0500
committerDmitry Torokhov <dmitry.torokhov@gmail.com>2026-09-13 18:17:31 -0700
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treef0b5f37b42fc13b9908a31b657c646b024231cdd /Documentation/block/cmdline-partition.rst
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Input: tsc2007 - read "ti,poll-period" as u32grafted
The "ti,poll-period" property is documented as a normal uint32 cell. The driver used a u64 helper, which makes the helper type disagree with the schema even though the stored value is still small. Read "ti,poll-period" with the u32 helper matching the documented DT cell size. Assisted-by: Codex:gpt-5-5 Signed-off-by: Rob Herring (Arm) <robh@kernel.org> Link: https://patch.msgid.link/20260831194352.1185860-1-robh@kernel.org Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
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+==============================================
+Embedded device command line partition parsing
+==============================================
+
+The "blkdevparts" command line option adds support for reading the
+block device partition table from the kernel command line.
+
+It is typically used for fixed block (eMMC) embedded devices.
+It has no MBR, so saves 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 uses fixed block device.
+ Its disk name is also fixed, such as: mmcblk0, mmcblk1, mmcblk0boot0.
+
+<size>
+ partition size, in bytes, such as: 512, 1m, 1G.
+ size may contain an optional suffix of (upper or lower case):
+
+ K, M, G, T, P, E.
+
+ "-" is used to denote all remaining space.
+
+<offset>
+ partition start address, in bytes.
+ offset may contain an optional suffix of (upper or lower case):
+
+ K, M, G, T, P, E.
+
+(part-name)
+ partition name. Kernel sends 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.
+
+ro
+ read-only. Flag the partition as read-only.
+
+Example:
+
+ eMMC disk names are "mmcblk0" and "mmcblk0boot0".
+
+ bootargs::
+
+ 'blkdevparts=mmcblk0:1G(data0),1G(data1),-;mmcblk0boot0:1m(boot)ro,-(kernel)'
+
+ dmesg::
+
+ mmcblk0: p1(data0) p2(data1) p3()
+ mmcblk0boot0: p1(boot) p2(kernel)