[PATCH v4 8/8] doc: uefi: Update the capsule update related documentation

[Sughosh Ganu]

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 V3:
* Rephrase the commit message to indicate that the doc changes are not
  just limited to adding the GUID values, but other info as well.
* Elaborate with an example on the relation between the dfu alt number
  and the image index 

 doc/develop/uefi/uefi.rst | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst
index fe337c88bd..d886635cc3 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 +333,26 @@ 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 things need to be defined in the board file for performing the
+capsule upadte. The first is defining the function set_dfu_alt_info in
+the board file. This function sets the environment variable
+dfu_alt_info. Instead of taking the variable from the environment, the
+capsule update feature requires that the variable be set through the
+board function, since that is more robust. Secondly, define GUID
+values and image index of the images that are to be updated through
+the capsule update feature in the board file. Both the values are to
+be defined as part of the fw_images 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
+
+
 Finally, the capsule update can be initiated by rebooting the board.
 
 Enabling Capsule Authentication
-- 
2.25.1