On 19/10/2020 15.56, 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=%U" to be used in bootargs, with the %U substitution > providing the UUID of the root device. > > For example, to substitute the GUID of the kernel partition: > > setenv bootargs "console=/dev/ttyS0 rootdev=%U/PARTNROFF=1 kern_guid=%U" > part uuid mmc 2:2 uuid > setenv bootargs_U $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 <s...@chromium.org> > --- > > README | 16 +++++++ > arch/Kconfig | 1 + > common/Kconfig.boot | 20 ++++++++ > common/bootm.c | 72 +++++++++++++++++++++++++++-- > include/bootm.h | 14 ++++-- > test/bootm.c | 110 ++++++++++++++++++++++++++++++++++++++++++-- > 6 files changed, 221 insertions(+), 12 deletions(-) > > diff --git a/README b/README > index 91c5a1a8fa3..263e31ab7f6 100644 > --- a/README > +++ b/README > @@ -3229,6 +3229,22 @@ List of environment variables (most likely not > complete): > > bootargs - Boot arguments when booting an RTOS image > > + bootargs_subst - Substitution parameters for bootargs. These are applied > after > + the commandline has been built. The format is: > + > + <key>=<value>[!<key>=<value>...] > + > + where > + <key> is a string to replace > + <value> is the value to replace it with (either a simple > + string or an environment variable starting with $ > + > + One use for this is to insert the root-disk UUID into the > + command line where bootargs contains "root=%U" > + > + part uuid mmc 2:2 uuid > + setenv cmdline_repl %U=$uuid
cmdline_repl seems to be stale, it should be bootargs_subst. But the whole paragraph seems stale, as you actually implement and test the bootargs_X approach. Anyway, this does seem useful, but I really question the choice of leaving %A in there if bootargs_A does not exist. It's hard if not impossible to create an environment variable whose value is empty, and I can easily imagine it would be useful to allow a %A to expand to nothing. So why not just use the usual semantics of requiring a double %% to put a single % in the output? It's probably quite rare that one would need that anyway. Rasmus
