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

[AKASHI Takahiro]

On Wed, Apr 13, 2022 at 12:38:05PM +0530, Sughosh Ganu wrote:
> 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?

This structure (not a variable like struct efi_fw_image foo_images[])
can only hold/represent one firmware image, right?
If so, efi_fw_image looks better.

> >
> > > +             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?

I hope that it will cover not only index, but example arrays of
struct efi_fw_image and struct efi_capsule_update_info
as well as an example "dfu_alto_info".

-Takahiro Akashi

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