[U-Boot] [U-Boot,v3,14/21] efi_loader: efi variable support

[Alexander Graf]

> Add EFI variable support, mapping to u-boot environment variables.
> Variables are pretty important for setting up boot order, among other
> things.  If the board supports saveenv, then it will be called in
> ExitBootServices() to persist variables set by the efi payload.  (For
> example, fallback.efi configuring BootOrder and BootXXXX load-option
> variables.)
> 
> Variables are *not* currently exposed at runtime, post ExitBootServices.
> On boards without a dedicated device for storage, which the loaded OS
> is not trying to also use, this is rather tricky.  One idea, at least
> for boards that can persist RAM across reboot, is to keep a "journal"
> of modified variables in RAM, and then turn halt into a reboot into
> u-boot, plus store variables, plus halt.  Whatever the solution, it
> likely involves some per-board support.
> 
> Mapping between EFI variables and u-boot variables:
> 
>   efi_$guid_$varname = {attributes}(type)value
> 
> For example:
> 
>   efi_8be4df61-93ca-11d2-aa0d-00e098032b8c_OsIndicationsSupported=
>      "{ro,boot,run}(blob)0000000000000000"
>   efi_8be4df61-93ca-11d2-aa0d-00e098032b8c_BootOrder=
>      "(blob)00010000"
> 
> The attributes are a comma separated list of these possible
> attributes:
> 
>   + ro   - read-only
>   + boot - boot-services access
>   + run  - runtime access
> 
> NOTE: with current implementation, no variables are available after
> ExitBootServices, and all are persisted (if possible).
> 
> If not specified, the attributes default to "{boot}".
> 
> The required type is one of:
> 
>   + utf8 - raw utf8 string
>   + blob - arbitrary length hex string
> 
> Signed-off-by: Rob Clark <robdclark at gmail.com>

Thanks, applied to efi-next

Alex