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

[Sughosh Ganu]

On Wed, 13 Apr 2022 at 11:48, AKASHI Takahiro
<takahiro.akashi at linaro.org> wrote:
>
> 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 at 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)?

Hmm, since this is to be an array of firmware images which should be
handled by the capsule update code, I used a plural form. Do you
prefer efi_fw_image instead?

>
> > +             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.

It can be added to this structure, yes. But we will also need to add
code in the capsule driver to update these fields accordingly. I can
take this up as a follow up task once the FWU series upstreaming is
done.

>
>
> > +     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.

I have added an example above for the raw images, as to how the image
index corresponds with the dfu alt number. Does it not suffice?

-sughosh

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