Re: [PATCH v11 15/15] FWU: doc: Add documentation for the FWU feature

Takahiro Akashi
2022-10-04T07:09:38Z

On Tue, Oct 04, 2022 at 12:10:27PM +0530, Sughosh Ganu wrote:
> hi Takahiro,
>
> On Tue, 4 Oct 2022 at 08:24, Takahiro Akashi <takahiro.akashi@linaro.org> wrote:
> >
> > Sughosh,
> >
> > On Wed, Sep 28, 2022 at 02:59:56PM +0530, Sughosh Ganu wrote:
> > > Add documentation for the FWU Multi Bank Update feature. The document
> > > describes the steps needed for setting up the platform for the
> > > feature, as well as steps for enabling the feature on the platform.
> > >
> > > Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
> > > ---
> > > Changes since V10:
> > > * Fix review comments suggested by Etienne
> > > * Add a paragraph in the capsule update section to highlight the
> > > difference in ImageIndex correlation with DFU alt num with FWU feature
> > > enabled
> > >
> > > doc/develop/uefi/fwu_updates.rst | 173 +++++++++++++++++++++++++++++++
> > > doc/develop/uefi/index.rst | 1 +
> > > doc/develop/uefi/uefi.rst | 10 ++
> > > 3 files changed, 184 insertions(+)
> > > create mode 100644 doc/develop/uefi/fwu_updates.rst
> > >
> > > diff --git a/doc/develop/uefi/fwu_updates.rst b/doc/develop/uefi/fwu_updates.rst
> > > new file mode 100644
> > > index 0000000000..292feceb9a
> > > --- /dev/null
> > > +++ b/doc/develop/uefi/fwu_updates.rst
> > > @@ -0,0 +1,173 @@
> > > +.. SPDX-License-Identifier: GPL-2.0+
> > > +.. Copyright (c) 2022 Linaro Limited
> > > +
> > > +FWU Multi Bank Updates in U-Boot
> > > +================================
> > > +
> > > +The FWU Multi Bank Update feature implements the firmware update
> > > +mechanism described in the PSA Firmware Update for A-profile Arm
> > > +Architecture specification [1]. Certain aspects of the Dependable
> > > +Boot specification [2] are also implemented. The feature provides a
> > > +mechanism to have multiple banks of updatable firmware images and for
> > > +updating the firmware images on the non-booted bank. On a successful
> > > +update, the platform boots from the updated bank on subsequent
> > > +boot. The UEFI capsule-on-disk update feature is used for performing
> > > +the actual updates of the updatable firmware images.
> > > +
> > > +The bookkeeping of the updatable images is done through a structure
> > > +called metadata. Currently, the FWU metadata supports identification
> > > +of images based on image GUIDs stored on a GPT partitioned storage
> > > +media. There are plans to extend the metadata structure for non GPT
> > > +partitioned devices as well.
> > > +
> > > +Accessing the FWU metadata is done through generic API's which are
> > > +defined in a driver which complies with the U-Boot's driver model. A
> > > +new uclass UCLASS_FWU_MDATA has been added for accessing the FWU
> > > +metadata. Individual drivers can be added based on the type of storage
> > > +media, and its partitioning method. Details of the storage device
> > > +containing the FWU metadata partitions are specified through a U-Boot
> > > +specific device tree property `fwu-mdata-store`. Please refer to
> > > +U-Boot `doc <doc/device-tree-bindings/firmware/fwu-mdata-gpt.yaml>`__
> > > +for the device tree bindings.
> > > +
> > > +Enabling the FWU Multi Bank Update feature
> > > +------------------------------------------
> > > +
> > > +The feature can be enabled by specifying the following configs::
> > > +
> > > + CONFIG_EFI_CAPSULE_ON_DISK=y
> > > + CONFIG_EFI_CAPSULE_FIRMWARE_MANAGEMENT=y
> > > + CONFIG_EFI_CAPSULE_FIRMWARE_RAW=y
> > > +
> > > + CONFIG_FWU_MULTI_BANK_UPDATE=y
> > > + CONFIG_CMD_FWU_METADATA=y
> > > + CONFIG_FWU_MDATA=y
> > > + CONFIG_FWU_MDATA_GPT_BLK=y
> > > + CONFIG_FWU_NUM_BANKS=<val>
> > > + CONFIG_FWU_NUM_IMAGES_PER_BANK=<val>
> > > +
> > > +in the .config file
> > > +
> > > +The first group of configuration settings enable the UEFI
> > > +capsule-on-disk update functionality. The second group of configs
> > > +enable the FWU Multi Bank Update functionality. Please refer to the
> > > +section :ref:`uefi_capsule_update_ref` for more details on generation
> > > +of the UEFI capsule.
> > > +
> > > +Setting up the device for GPT partitioned storage
> > > +-------------------------------------------------
> > > +
> > > +Before enabling the functionality in U-Boot, a GPT partitioned storage
> > > +device is required. Assuming a GPT partitioned storage device, the
> > > +storage media needs to be partitioned with the correct number of
> > > +partitions, given the number of banks and number of images per bank
> > > +that the platform is going to support. Each updatable firmware image
> > > +will be stored on a separate partition. In addition, the two copies
> > > +of the FWU metadata will be stored on two separate partitions.
> > > +
> > > +As an example, a platform supporting two banks with each bank
> > > +containing three images would need to have 2 * 3 = 6 partitions plus
> > > +the two metadata partitions, or 8 partitions. In addition the storage
> > > +media can have additional partitions of non-updatable images, like the
> > > +EFI System Partition(ESP), a partition for the root file system
> > > +etc. An example list of images on the storage medium would be
> > > +
> > > +* FWU metadata 1
> > > +* U-Boot 1
> > > +* OP-TEE 1
> > > +* FWU metadata 2
> > > +* OP-TEE 2
> > > +* U-Boot 2
> > > +* ESP
> > > +* rootfs
> > > +
> > > +When generating the partitions, a few aspects need to be taken care
> > > +of. Each GPT partition entry in the GPT header has two GUIDs::
> > > +
> > > +* PartitionTypeGUID
> > > +* UniquePartitionGUID
> > > +
> > > +The PartitionTypeGUID value should correspond to the
> > > +``image_type_uuid`` field of the FWU metadata. This field is used to
> > > +identify a given type of updatable firmware image, e.g. U-Boot,
> > > +OP-TEE, FIP etc. This GUID should also be used for specifying the
> > > +`--guid` parameter when generating the capsule.
> > > +
> > > +The UniquePartitionGUID value should correspond to the ``image_uuid``
> > > +field in the FWU metadata. This GUID is used to identify images of a
> > > +given image type in different banks.
> >
> > Well, what is not clear to me here is:
> > - who is responsible to set up FWU metadata and when
>
> Initially, when the board is being provisioned, the metadata is
> supposed to be installed on two separate partitions. This is described
> under "Setting up the device for GPT partitioned storage".
>
> > - how FWU metadata is related to fw_images and update_info
> > which are used in normal case, which is mentioned in develop/uefi/uefi.rst
>
> The entire update process is the same as the UEFI capsule update. This
> is being highlighted in the first paragraph under "Performing the
> Update".

I think of developers.

For instance, as I mentioned above, image_type_uuid/image_index in FWU metadata
must match with the ones in fw_images.
And how about update_info, especially dfu_string? This field won't be used
in A/B update IIUC.
There are a couple of points that developers should be aware.
That is why I suggested the whole explanation is in one place.

> I have also added a paragraph under "Performing the update"
> which specifies how the image index value used with the FWU feature
> enabled is different from the normal capsule update.
>
> >
> > I know the whole text here is dedicated to A/B update, but I think
> > it would also be helpful to have a single document which covers both cases
> > for developers to understand how differently FWU is configured for those cases.
>
> I would think that it would be more clear to have a separate document
> for the FWU updates. In any case, the fwu_updates.rst is under the
> same directory as the uefi.rst which explains the normal capsule
> update functionality. There would also be addition of the section for
> the FWU updates on platforms using MTD based devices. So I think it
> would be better to keep the documents separate. Even if we move the
> content in fwu_updates.rst under uefi.rst, the actual update process
> would still be explained by the section under
> 'uefi_capsule_update_ref'. Do you see difficulty in understanding the
> FWU update feature being kept in a separate file?

Yes.

I don't care whether the text is contained in a physically-single document,
but do expect that the normal case and A/B update are described (in different
sections) under the logically-same chapter for better understanding of differences.

-Takahiro Akashi

> -sughosh
>
> >
> > -Takahiro Akashi
> >
> > > +
> > > +Similarly, the FWU specification defines the GUID value to be used
> > > +for the metadata partitions. This would be the PartitionTypeGUID for
> > > +the metadata partitions.
> > > +
> > > +When generating the metadata, the ``image_type_uuid`` and the
> > > +``image_uuid`` values should match the *PartitionTypeGUID* and the
> > > +*UniquePartitionGUID* values respectively.
> > > +
> > > +Performing the Update
> > > +---------------------
> > > +
> > > +Once the storage media has been partitioned and populated with the
> > > +metadata partitions, the UEFI capsule-on-disk update functionality can
> > > +be used for performing the update. Refer to the section
> > > +:ref:`uefi_capsule_update_ref` for details on how the update can be
> > > +invoked.
> > > +
> > > +On a successful update, the FWU metadata gets updated to reflect the
> > > +bank from which the platform would be booting on subsequent boot.
> > > +
> > > +Based on the value of bit15 of the Flags member of the capsule header,
> > > +the updated images would either be accepted by the U-Boot's UEFI
> > > +implementation, or by the Operating System. If the Operating System is
> > > +accepting the firmware images, it does so by generating an empty
> > > +*accept* capsule. The Operating System can also reject the updated
> > > +firmware by generating a *revert* capsule. The empty capsule can be
> > > +applied by using the exact same procedure used for performing the
> > > +capsule-on-disk update.
> > > +
> > > +The task of accepting the different firmware images, post an update
> > > +may be done by multiple, separate components in the Operating
> > > +System. To help identify the firmware image that is being accepted,
> > > +the accept capsule passes the image GUID of the firmware image being
> > > +accepted. The relevant code in U-Boot then sets the Accept bit of the
> > > +corresponding firmware image for which the accept capsule was
> > > +found. Only when all the firmware components in a bank have been
> > > +accepted does the platform transition from trial state to regular
> > > +state.
> > > +
> > > +The revert capsule on the other hand does not pass any image GUID,
> > > +since reverting any image of the bank has the same result of the
> > > +platform booting from the other bank on subsequent boot.
> > > +
> > > +Generating an empty capsule
> > > +---------------------------
> > > +
> > > +The empty capsule can be generated using the mkeficapsule utility. To
> > > +build the tool, enable::
> > > +
> > > + CONFIG_TOOLS_MKEFICAPSULE=y
> > > +
> > > +Run the following commands to generate the accept/revert capsules::
> > > +
> > > +.. code-block:: bash
> > > +
> > > + $ ./tools/mkeficapsule \
> > > + [--fw-accept --guid <image guid>] | \
> > > + [--fw-revert] \
> > > + <capsule_file_name>
> > > +
> > > +Some examples of using the mkeficapsule tool for generation of the
> > > +empty capsule would be::
> > > +
> > > +.. code-block:: bash
> > > +
> > > + $ ./tools/mkeficapsule --fw-accept --guid <image guid> \
> > > + <accept_capsule_name>
> > > + $ ./tools/mkeficapsule --fw-revert <revert_capsule_name>
> > > +
> > > +Links
> > > +-----
> > > +
> > > +* [1] https://developer.arm.com/documentation/den0118/a/ - FWU Specification
> > > +* [2] https://git.codelinaro.org/linaro/dependable-boot/mbfw/uploads/6f7ddfe3be24e18d4319e108a758d02e/mbfw.pdf - Dependable Boot Specification
> > > diff --git a/doc/develop/uefi/index.rst b/doc/develop/uefi/index.rst
> > > index 7e65dbc5d5..e26b1fbe05 100644
> > > --- a/doc/develop/uefi/index.rst
> > > +++ b/doc/develop/uefi/index.rst
> > > @@ -13,3 +13,4 @@ can be run an UEFI payload.
> > > uefi.rst
> > > u-boot_on_efi.rst
> > > iscsi.rst
> > > + fwu_updates.rst
> > > diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst
> > > index 941e427093..b5c83db65a 100644
> > > --- a/doc/develop/uefi/uefi.rst
> > > +++ b/doc/develop/uefi/uefi.rst
> > > @@ -277,6 +277,8 @@ Enable ``CONFIG_OPTEE``, ``CONFIG_CMD_OPTEE_RPMB`` and ``CONFIG_EFI_MM_COMM_TEE`
> > >
> > > [1] https://optee.readthedocs.io/en/latest/building/efi_vars/stmm.html
> > >
> > > +.. _uefi_capsule_update_ref:
> > > +
> > > Enabling UEFI Capsule Update feature
> > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >
> > > @@ -377,6 +379,14 @@ following command::
> > >
> > > dfu list
> > >
> > > +When the FWU Multi Bank Update feature is enabled on the platform, the
> > > +image index is used only to identify the image index with the image
> > > +GUID. The image index would not correspond to the dfu alt number. This
> > > +is because the FWU feature supports multiple partitions(banks) of
> > > +updatable images, and the actual dfu alt number to which the image is
> > > +to be written to is determined at runtime, based on the value of the
> > > +update bank to which the image is to be written.
> > > +
> > > When using the FMP for FIT images, the image index value needs to be
> > > set to 1.
> > >
> > > --
> > > 2.34.1
> > >