[PATCH v2 12/12] bootm: Support string substitution in bootargs

[Tom Rini]

On Thu, Nov 05, 2020 at 10:33:48AM -0700, Simon Glass wrote:

> In some cases it is necessary to pass parameters to Linux so that it will
> boot correctly. For example, the rootdev parameter is often used to
> specify the root device. However the root device may change depending on
> whence U-Boot loads the kernel. At present it is necessary to build up
> the command line by adding device strings to it one by one.
> 
> It is often more convenient to provide a template for bootargs, with
> U-Boot doing the substitution from other environment variables.
> 
> Add a way to substitute strings in the bootargs variable. This allows
> things like "rootdev=${rootdev}" to be used in bootargs, with the
> ${rootdev} substitution providing the UUID of the root device.
> 
> For example, to substitute the GUID of the kernel partition:
> 
>   setenv bootargs "console=/dev/ttyS0 rootdev=${uuid}/PARTNROFF=1
> 		kern_guid=${uuid}"
>   part uuid mmc 2:2 uuid
>   bootm
> 
> This is particularly useful when the command line from another place. For
> example, Chrome OS stores the command line next to the kernel itself. It
> depends on the kernel version being used as well as the hardware features,
> so it is extremely difficult to devise a U-Boot script that works on all
> boards and kernel versions. With this feature, the command line can be
> read from disk and used directly, with a few substitutions set up.
> 
> Signed-off-by: Simon Glass <sjg at chromium.org>

Applied to u-boot/next, thanks!

-- 
Tom
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