doc: uefi: document dynamic UUID generation

Document how platforms can generate GUIDs at runtime rather than
maintaining a list of UUIDs per-board.

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>

diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst
index d450b12bf801a638b967753bd6ed7e63da694430..94482758573156f50d7aeb0c962d8d2b27649b37 100644 (file)
--- a/doc/develop/uefi/uefi.rst
+++ b/doc/develop/uefi/uefi.rst
@@ -449,6 +449,33 @@ practice. Getting this information from the firmware itself is more
 secure, assuming the firmware has been verified by a previous stage
 boot loader.
 
+Dynamic Firmware Update GUIDs
+*****************************
+
+The image_type_id contains a GUID value which is specific to the image
+and board being updated, that is to say it should uniquely identify the
+board model (and revision if relevant) and image pair. Traditionally,
+these GUIDs are generated manually and hardcoded on a per-board basis,
+however this scheme makes it difficult to scale up to support many
+boards.
+
+To address this, v5 GUIDs can be used to generate board-specific GUIDs
+at runtime, based on the board's devicetree root compatible
+(e.g. "qcom,qrb5165-rb5").
+
+These strings are combined with the fw_image name to generate GUIDs for
+each image. Support for dynamic UUIDs can be enabled by generating a new
+namespace UUID and setting EFI_CAPSULE_NAMESPACE_GUID to it. Dynamic GUID
+generation is only enabled if the image_type_id property is unset for your
+firmware images, this is to avoid breaking existing boards with hardcoded
+GUIDs.
+
+The mkeficapsule tool can be used to determine the GUIDs for a particular
+board and image. It can be found in the tools directory.
+
+Firmware update images
+**********************
+
 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