Re: [PATCH] dt-bindings: u-boot: Add a few more options bindings

[Rob Herring <robh@kernel.org>]

On Fri, Nov 19, 2021 at 6:04 PM Simon Glass <sjg@chromium.org> wrote:
>
> This adds three new options with varying degree of interest / precedent.

Send these to devicetree-spec list so it's not in the flood of
devicetree-discuss.

>
> This being sent to the mailing list since it might attract more review.
> A PR will be sent when this has had some review. That is why the file
> path is set up for https://github.com/devicetree-org/dt-schema rather
> than the Linux kernel.
>
> Signed-off-by: Simon Glass <sjg@chromium.org>
> ---
>
>  schemas/options/u-boot.yaml | 51 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
>
> diff --git a/schemas/options/u-boot.yaml b/schemas/options/u-boot.yaml
> index 71dfda7..b8bdec1 100644
> --- a/schemas/options/u-boot.yaml
> +++ b/schemas/options/u-boot.yaml
> @@ -71,6 +71,37 @@ properties:
>        2: use simplified command line (e.g. avoid hush)
>        3... reserved
>
> +  load-environment:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    default: 1
> +    maximum: 1
> +    description: |
> +      This allows control over whether U-Boot loads its environment after
> +      relocation. This normally happens automatically, but can pose a security
> +      risk, so disabling it in certain situations is useful.
> +
> +      Note: This could be a boolean. It is defined as an integer since that
> +      allows changing the value without resizing the devicetree. I'm not sure
> +      how ugly that is, but IMO the fact that 'false' boolean values are
> +      represented by being missing is a bit of a pain. One must either add or

But they do save space. ;)

> +      delete the property.
> +
> +      Values:
> +
> +      0: don't load the environment
> +      1: do load the environment
> +
> +  no-apm-final:
> +    $ref: /schemas/types.yaml#/definitions/flag
> +    description: |
> +      For devices running on coreboot, this tells U-Boot not to lock down the
> +      Intel Management Engine (ME) registers. This allows U-Boot to access the
> +      hardware more fully for platforms that need it.
> +
> +      Absence of this property indicates that the ME registers should be locked
> +      down as part of U-Boot's start-up sequence and before the command line is
> +      available.

Perhaps prefix with 'intel' given it is Intel specific.

> +
>    silent-console:
>      $ref: /schemas/types.yaml#/definitions/uint32
>      default: 0
> @@ -88,6 +119,23 @@ properties:
>          enabled)
>        2: console output is suppressed and not recorded
>
> +  spl-payload-offset:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    default: 0
> +    description: |
> +      If present (and SPL is controlled by the devicetree), this allows the
> +      offset of the SPL payload (typically U-Boot) to be specified. The offset
> +      is in bytes from the start of the media (typically SPI flash).
> +
> +      Note: This is quite widely used in U-Boot, but since v2018.01 it is
> +      possible to use Binman instead, to provide this offset (and various
> +      others) to SPL, or even to U-Boot proper. So far I have not tried sending
> +      the Binman bindings upstream, but perhaps that should be done instead.

At this point, you are the upstream for binman...

> +
> +      See here for details:
> +
> +      https://u-boot.readthedocs.io/en/latest/develop/package/binman.html#image-description-format
> +
>  required:
>    - compatible
>
> @@ -101,6 +149,9 @@ examples:
>          bootcmd = "vboot go auto";
>          bootdelay-sec = <(-1)>;
>          bootsecure = <1>;
> +        load-environment = <0>;
> +        no-apm-final;
>          silent-console = <1>;
> +        spl-payload-offset = <0x40000>;   /* 256K */
>        };
>      };
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>