[PATCH 1/2] env: allow environment to be amended from control dtb

[Rasmus Villemoes]

On 21/04/2021 09.14, Simon Glass wrote:
> Hi Rasmus,
> 
> On Wed, 14 Apr 2021 at 10:43, Rasmus Villemoes
> <rasmus.villemoes at prevas.dk> wrote:
>>
>> It can be useful to use the same U-Boot binary for multiple purposes,
>> say the normal one, one for developers that allow breaking into the
>> U-Boot shell, and one for use during bootstrapping which runs a
>> special-purpose bootcmd. Or one can have several board variants that
>> can share almost all boot logic, but just needs a few tweaks in the
>> variables used by the boot script.
>>
>> To that end, allow the control dtb to contain a /config/enviroment
>> node (or whatever one puts in fdt_env_path variable), whose
>> property/value pairs are used to update the run-time environment after
>> it has been loaded from its persistent location.
>>
>> The indirection via fdt_env_path is for maximum flexibility - for
>> example, should the user wish (or board logic dictate) that the values
>> in the DTB should no longer be applied, one simply needs to delete the
>> fdt_env_path variable; that can even be done automatically by
>> including a
>>
>>   fdt_env_path = "";
>>
>> property in the DTB node.
>>
>> Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
>> ---
>>  common/board_r.c      |  2 ++
>>  env/Kconfig           | 18 ++++++++++++++++++
>>  env/common.c          | 23 +++++++++++++++++++++++
>>  include/env.h         | 15 +++++++++++++++
>>  include/env_default.h |  3 +++
>>  5 files changed, 61 insertions(+)
>>
> 
> Reviewed-by: Simon Glass <sjg at chromium.org>
> 
> Some suggestions below
> 
>> diff --git a/common/board_r.c b/common/board_r.c
>> index c835ff8e26..3f82404772 100644
>> --- a/common/board_r.c
>> +++ b/common/board_r.c
>> @@ -459,6 +459,8 @@ static int initr_env(void)
>>         else
>>                 env_set_default(NULL, 0);
>>
>> +       env_import_fdt();
>> +
>>         if (IS_ENABLED(CONFIG_OF_CONTROL))
>>                 env_set_hex("fdtcontroladdr",
>>                             (unsigned long)map_to_sysmem(gd->fdt_blob));
>> diff --git a/env/Kconfig b/env/Kconfig
>> index b473d7cfe1..aa800e37ce 100644
>> --- a/env/Kconfig
>> +++ b/env/Kconfig
>> @@ -647,6 +647,24 @@ config DELAY_ENVIRONMENT
>>           later by U-Boot code. With CONFIG_OF_CONTROL this is instead
>>           controlled by the value of /config/load-environment.
>>
>> +config ENV_IMPORT_FDT
>> +       bool "Amend environment by FDT properties"
>> +       depends on OF_CONTROL
>> +       help
>> +         If selected, after the environment has been loaded from its
>> +         persistent location, the "env_fdt_path" variable is looked
>> +         up and used as a path to a node in the control DTB. The
>> +         property/value pairs in that node is then used to update the
>> +         run-time environment. This can be useful to use the same
>> +         U-Boot binary with different board variants.
>> +
>> +config ENV_FDT_PATH
>> +       string "Default value for env_fdt_path variable"
>> +       depends on ENV_IMPORT_FDT
>> +       default "/config/environment"
>> +       help
>> +         The initial value of the env_fdt_path variable.
>> +
>>  config ENV_APPEND
>>         bool "Always append the environment with new data"
>>         default n
>> diff --git a/env/common.c b/env/common.c
>> index 2ee423beb5..af45e561ce 100644
>> --- a/env/common.c
>> +++ b/env/common.c
>> @@ -345,3 +345,26 @@ int env_complete(char *var, int maxv, char *cmdv[], int bufsz, char *buf,
>>         return found;
>>  }
>>  #endif
>> +
>> +#ifdef CONFIG_ENV_IMPORT_FDT
>> +void env_import_fdt(void)
>> +{
>> +       const void *blob = gd->fdt_blob;
>> +       const char *path;
>> +       int offset, prop;
>> +
>> +       path = env_get("env_fdt_path");
>> +       if (!path || !path[0])
>> +               return;
> 
> How about returning an error code indicating what happened?

I considered that, but I'm not sure what the (single) caller would do
with that. Not having env_fdt_path set is a supported use case as I
explain. So here it's not really an error. However, if env_fdt_path is
set, but there's no such node in the DT blob, it might be worth printing
a warning (i.e. in the "offset < 0" case below).

>> +       offset = fdt_path_offset(blob, path);
> 
> Could we use the livetree API here (ofnode)?

Dunno, what's that? Have U-Boot started deserializing the FDT blob like
the linux kernel does and build an in-memory representation that's
easier to traverse?

Thanks,
Rasmus