bootm: Support string substitution in bootargs
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=${uuid}"
part uuid mmc 2:2 uuid
bootm
This is particularly useful when the command line from another place. For
example, Chrome OS stores the command line next to the kernel itself. It
depends on the kernel version being used as well as the hardware features,
so it is extremely difficult to devise a U-Boot script that works on all
boards and kernel versions. With this feature, the command line can be
read from disk and used directly, with a few substitutions set up.
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Kconfig.boot b/common/Kconfig.boot
index 3f6d9c1..58e9854 100644
--- a/common/Kconfig.boot
+++ b/common/Kconfig.boot
@@ -865,6 +865,23 @@
CONFIG_BOOTARGS goes into the environment value "bootargs". Note that
this value will also override the "chosen" node in FDT blob.
+config BOOTARGS_SUBST
+ bool "Support substituting strings in boot arguments"
+ help
+ This allows substituting string values in the boot arguments. These
+ are applied after the commandline has been built.
+
+ One use for this is to insert the root-disk UUID into the command
+ line where bootargs contains "root=${uuid}"
+
+ setenv bootargs "console= root=${uuid}"
+ # Set the 'uuid' environment variable
+ part uuid mmc 2:2 uuid
+
+ # Command-line substitution will put the real uuid into the
+ # kernel command line
+ bootm
+
config USE_BOOTCOMMAND
bool "Enable a default value for bootcmd"
help