On 05/23/2014 05:41 PM, Kevin Hilman wrote:

By default, add some padding to the DT blobs to facilitate later
patching.

An example need for DTB patching is the need to modifiy the command
line on platforms where ATAGS are not (or cannot) be used to pass the
commandline.  For example, we do not support a big-endian kernel
reading ATAGS from a little-endian u-boot, so the only way to pass a
command line in the DT.

Also, without ATAG support (or if u-boot was built without
CONFIG_INITRD_TAG) the only way to pass an initrd is by adding an
initrd= option to command line (in the DT).

Therefore, to facilitate adding to the DT command line directly in the
DTB, add some padding.

Cc: Nicolas Pitre <redacted>
Cc: Stephen Warren <redacted>
Cc: Thomas Petazzoni <redacted>
Signed-off-by: Kevin Hilman <redacted>
---
I kinda pulled 64 bytes out of the air here since it's enough to add
some common things to the commandline like debug, earlyprink
initrd=<addr>,<size>, etc., but I'm certainlly not opposed to more
padding.

Conceptually,
Acked-by: Stephen Warren <redacted>

But I would expect a pad of something like 4KB to be more future-proof.
U-Boot appears to use 4KB on ARM at least:

./arch/arm/dts/Makefile:37:DTC_FLAGS += -R 4 -p 0x1000