Re: [PATCH v6 8/8] doc: uefi: Update the capsule update related documentation

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Tue, Apr 12, 2022 at 06:34:47PM +0530, Sughosh Ganu wrote:
> Update the capsule update functionality related documentation to
> refect the additional definitions that need to be made per platform
> for supporting the capsule update feature.
> 
> Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
> ---
> 
> Changes since V5: None
> 
>  doc/develop/uefi/uefi.rst | 51 +++++++++++++++++++++++++++++++++++++--
>  1 file changed, 49 insertions(+), 2 deletions(-)
> 
> diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst
> index fe337c88bd..b766aecf67 100644
> --- a/doc/develop/uefi/uefi.rst
> +++ b/doc/develop/uefi/uefi.rst
> @@ -312,8 +312,8 @@ Run the following command
>  .. code-block:: console
>  
>      $ mkeficapsule \
> -      --index 1 --instance 0 \
> -      [--fit <FIT image> | --raw <raw image>] \
> +      --index <index> --instance 0 \
> +      --guid <image GUID> \
>        <capsule_file_name>
>  
>  Performing the update
> @@ -333,6 +333,53 @@ won't be taken over across the reboot. If this is the case, you can skip
>  this feature check with the Kconfig option (CONFIG_EFI_IGNORE_OSINDICATIONS)
>  set.
>  
> +A few values need to be defined in the board file for performing the
> +capsule update. These values are defined in the board file by
> +initialisation of a structure which provides information needed for
> +capsule updates. The following structures have been defined for
> +containing the image related information
> +
> +.. code-block:: c
> +
> +	struct efi_fw_images {

Why "images" (in the plural)?

> +		efi_guid_t image_type_id;
> +		u16 *fw_name;
> +		u8 image_index;
> +	};

Why not add "version" and "last_attempt_version" which is expected
to be easily implemented in this structure.


> +	struct efi_capsule_update_info {
> +		const char *dfu_string;
> +		struct efi_fw_images *images;
> +	};
> +
> +
> +A string is defined which is to be used for populating the
> +dfu_alt_info variable. This string is used by the function
> +set_dfu_alt_info. Instead of taking the variable from the environment,
> +the capsule update feature requires that the variable be set through
> +the function, since that is more robust. Allowing the user to change
> +the location of the firmware updates is not a very secure
> +practice. Getting this information from the firmware itself is more
> +secure, assuming the firmware has been verified by a previous stage
> +boot loader.
> +
> +The firmware images structure defines the GUID values, image index
> +values and the name of the images that are to be updated through
> +the capsule update feature. These values are to be defined as part of
> +an array. These GUID values would be used by the Firmware Management
> +Protocol(FMP) to populate the image descriptor array and also
> +displayed as part of the ESRT table. The image index values defined in
> +the array should be one greater than the dfu alt number that
> +corresponds to the firmware image. So, if the dfu alt number for an
> +image is 2, the value of image index in the fw_images array for that
> +image should be 3. The dfu alt number can be obtained by running the
> +following command::
> +
> +    dfu list
> +
> +When using the FMP for FIT images, the image index value needs to be
> +set to 1.

The explanation would be correct, but it's not quite easy to understand,
in particular, index in case of raw.
You should add some examples here.

-Takahiro Akashi

> +
>  Finally, the capsule update can be initiated by rebooting the board.
>  
>  Enabling Capsule Authentication
> -- 
> 2.25.1
>