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

[Sughosh Ganu <sughosh.ganu@linaro.org>]

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 {
+		efi_guid_t image_type_id;
+		u16 *fw_name;
+		u8 image_index;
+	};
+
+	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.
+
 Finally, the capsule update can be initiated by rebooting the board.
 
 Enabling Capsule Authentication
-- 
2.25.1