--- /dev/null
+.. SPDX-License-Identifier: GPL-2.0+
+.. Copyright (C) 2020, Linaro Limited
+
+Enabling UEFI Capsule Update feature
+------------------------------------
+
+Support has been added for the UEFI capsule update feature which
+enables updating the U-Boot image using the UEFI firmware management
+protocol (fmp). The capsules are not passed to the firmware through
+the UpdateCapsule runtime service. Instead, capsule-on-disk
+functionality is used for fetching the capsule from the EFI System
+Partition (ESP) by placing the capsule file under the
+\EFI\UpdateCapsule directory.
+
+Currently, support has been added on the QEMU ARM64 virt platform for
+updating the U-Boot binary as a raw image when the platform is booted
+in non-secure mode, i.e. with CONFIG_TFABOOT disabled. For this
+configuration, the QEMU platform needs to be booted with
+'secure=off'. The U-Boot binary placed on the first bank of the NOR
+flash at offset 0x0. The U-Boot environment is placed on the second
+NOR flash bank at offset 0x4000000.
+
+The capsule update feature is enabled with the following configuration
+settings::
+
+ CONFIG_MTD=y
+ CONFIG_FLASH_CFI_MTD=y
+ CONFIG_CMD_MTDPARTS=y
+ CONFIG_CMD_DFU=y
+ CONFIG_DFU_MTD=y
+ CONFIG_PCI_INIT_R=y
+ CONFIG_EFI_CAPSULE_ON_DISK=y
+ CONFIG_EFI_CAPSULE_FIRMWARE_MANAGEMENT=y
+ CONFIG_EFI_CAPSULE_FIRMWARE=y
+ CONFIG_EFI_CAPSULE_FIRMWARE_RAW=y
+ CONFIG_EFI_CAPSULE_FMP_HEADER=y
+
+In addition, the following config needs to be disabled(QEMU ARM specific)::
+
+ CONFIG_TFABOOT
+
+The capsule file can be generated by using the GenerateCapsule.py
+script in EDKII::
+
+ $ ./BaseTools/BinWrappers/PosixLike/GenerateCapsule -e -o \
+ <capsule_file_name> --fw-version <val> --lsv <val> --guid \
+ e2bb9c06-70e9-4b14-97a3-5a7913176e3f --verbose --update-image-index \
+ <val> --verbose <u-boot.bin>
+
+The above is a wrapper script(GenerateCapsule) which eventually calls
+the actual GenerateCapsule.py script.
+
+As per the UEFI specification, the capsule file needs to be placed on
+the EFI System Partition, under the \EFI\UpdateCapsule directory. The
+EFI System Partition can be a virtio-blk-device.
+
+Before initiating the firmware update, the efi variables BootNext,
+BootXXXX and OsIndications need to be set. The BootXXXX variable needs
+to be pointing to the EFI System Partition which contains the capsule
+file. The BootNext, BootXXXX and OsIndications variables can be set
+using the following commands::
+
+ => efidebug boot add 0 Boot0000 virtio 0:1 <capsule_file_name>
+ => efidebug boot next 0
+ => setenv -e -nv -bs -rt -v OsIndications =0x04
+ => saveenv
+
+Finally, the capsule update can be initiated with the following
+command::
+
+ => efidebug capsule disk-update
+
+The updated U-Boot image will be booted on subsequent boot.
+
+Enabling Capsule Authentication
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The UEFI specification defines a way of authenticating the capsule to
+be updated by verifying the capsule signature. The capsule signature
+is computed and prepended to the capsule payload at the time of
+capsule generation. This signature is then verified by using the
+public key stored as part of the X509 certificate. This certificate is
+in the form of an efi signature list (esl) file, which is embedded as
+part of the platform's device tree blob using the mkeficapsule
+utility.
+
+On the QEMU virt platforms, the device-tree is generated on the fly
+based on the devices configured. This device tree is then passed on to
+the various software components booting on the platform, including
+U-Boot. Therefore, on the QEMU virt platform, the signatute is
+embedded on an overlay. This overlay is then applied at runtime to the
+base platform device-tree. Steps needed for embedding the esl file in
+the overlay are highlighted below.
+
+The capsule authentication feature can be enabled through the
+following config, in addition to the configs listed above for capsule
+update::
+
+ CONFIG_EFI_CAPSULE_AUTHENTICATE=y
+
+The public and private keys used for the signing process are generated
+and used by the steps highlighted below::
+
+ 1. Install utility commands on your host
+ * OPENSSL
+ * efitools
+
+ 2. Create signing keys and certificate files on your host
+
+ $ openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=CRT/ \
+ -keyout CRT.key -out CRT.crt -nodes -days 365
+ $ cert-to-efi-sig-list CRT.crt CRT.esl
+
+ $ openssl x509 -in CRT.crt -out CRT.cer -outform DER
+ $ openssl x509 -inform DER -in CRT.cer -outform PEM -out CRT.pub.pem
+
+ $ openssl pkcs12 -export -out CRT.pfx -inkey CRT.key -in CRT.crt
+ $ openssl pkcs12 -in CRT.pfx -nodes -out CRT.pem
+
+The capsule file can be generated by using the GenerateCapsule.py
+script in EDKII::
+
+ $ ./BaseTools/BinWrappers/PosixLike/GenerateCapsule -e -o \
+ <capsule_file_name> --monotonic-count <val> --fw-version \
+ <val> --lsv <val> --guid \
+ e2bb9c06-70e9-4b14-97a3-5a7913176e3f --verbose \
+ --update-image-index <val> --signer-private-cert \
+ /path/to/CRT.pem --trusted-public-cert \
+ /path/to/CRT.pub.pem --other-public-cert /path/to/CRT.pub.pem \
+ <u-boot.bin>
+
+Place the capsule generated in the above step on the EFI System
+Partition under the EFI/UpdateCapsule directory
+
+For embedding the public key certificate, the following steps need to
+be followed::
+
+ 1. Generate a skeleton overlay dts file, with a single fragment
+ node and an empty __overlay__ node
+
+ A typical skeleton overlay file will look like this
+
+ /dts-v1/;
+ /plugin/;
+
+ / {
+ fragment@0 {
+ target-path = "/";
+ __overlay__ {
+ };
+ };
+ };
+
+
+ 2. Convert the dts to a corresponding dtb with the following
+ command
+ ./scripts/dtc/dtc -@ -I dts -O dtb -o <ov_dtb_file_name> \
+ <dts_file>
+
+ 3. Run the dtb file generated above through the mkeficapsule tool
+ in U-Boot
+ ./tools/mkeficapsule -O <pub_key.esl> -D <ov_dtb>
+
+Running the above command results in the creation of a 'signature'
+node in the dtb, under which the public key is stored as a
+'capsule-key' property. The '-O' option is to be used since the
+public key certificate(esl) file is being embedded in an overlay.
+
+The dtb file embedded with the certificate is now to be placed on an
+EFI System Partition. This would then be loaded and "merged" with the
+base platform flattened device-tree(dtb) at runtime.
+
+Build U-Boot with the following steps(QEMU ARM64)::
+
+ $ make qemu_arm64_defconfig
+ $ make menuconfig
+ Disable CONFIG_TFABOOT
+ Enable CONFIG_EFI_CAPSULE_AUTHENTICATE
+ Enable all configs needed for capsule update(listed above)
+ $ make all
+
+Boot the platform and perform the following steps on the U-Boot
+command line::
+
+ 1. Enable capsule authentication by setting the following env
+ variable
+
+ => setenv capsule_authentication_enabled 1
+ => saveenv
+
+ 2. Load the overlay dtb to memory and merge it with the base fdt
+
+ => fatload virtio 0:1 <$fdtovaddr> EFI/<ov_dtb_file>
+ => fdt addr $fdtcontroladdr
+ => fdt resize <size_of_ov_dtb_file>
+ => fdt apply <$fdtovaddr>
+
+ 3. Set the following environment and UEFI boot variables
+
+ => setenv -e -nv -bs -rt -v OsIndications =0x04
+ => efidebug boot add 0 Boot0000 virtio 0:1 <capsule_file_name>
+ => efidebug boot next 0
+ => saveenv
+
+ 4. Finally, the capsule update can be initiated with the following
+ command
+
+ => efidebug capsule disk-update
+
+On subsequent reboot, the platform should boot the updated U-Boot binary.
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