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USB Type-C Power Delivery (PD) Firmware

Some Type-C Port Controller (TCPC) chips in ChromeOS Devices are programmed with a firmware component when shipped out of the factory. This firmware (sometimes called PD firmware) may be updateable in the field. The firmware update for TCPC chips happen as part of the Embedded Controller (EC) Software Sync process which in turn happens as part of verified boot.

PD Firmware update overview

PD Firmware update is managed by depthcharge. When the system boots up, depthcharge performs EC software sync to update the RW firmware of EC and any peripherals that are connected to EC. During the EC software sync, PD firmware update is performed after the EC's firmware is updated and has jumped to RW section successfully.

PD Firmware binary along with a matching PD firmware hash is packaged into Coreboot File System (CBFS) as part of building the AP firmware. PD Firmware hash includes firmware version information. When the system boots up using the updated AP firmware, depthcharge requests the firmware version from the live TCPC chip. If the firmware version returned by the TCPC chip differs from the firmware version built into the CBFS, the firmware update is performed. PD firmware update progress is displayed using a splash screen with the following message:

Your system is applying a critical update.

Please do not turn it off.

Once the PD firmware update is complete, EC is rebooted to RO so that the TCPC chips are reset.

Packaging PD firmware into CBFS

Packaging PD firmware into CBFS involves the following steps:

Upload the new PD firmware blob to Google Cloud Platform Storage

When the TCPC chip vendor supplies the new PD firmware binary blob, it is archived as a tarball and uploaded to Google Cloud Platform Storage. The tarball name must be the same as the new PD firmware package name in ebuild.

eg. parade-ps8751a3-firmware-68.tar.xz

In the above example, parade-ps8751a3-firmware-68 is the new PD firmware package and the tarball name matches that. Please refer below example showing the contents and the layout of the tarball.

$ tar -tf parade-ps8751a3-firmware-68.tar.xz

The PD firmware blob name inside the tarball must follow a specific format depending on the TCPC chip type. The ebuilds that install PD firmware blob into CBFS use this name format to identify the firmware blob.

For Parade TCPC chips, the format is: {product_id}_{hardware_version}_0x{hex_firmware_version}.bin

eg. ps8751_a3_0x44.bin and the referring parade ebuild

For Analogix TCPC chips, the format is: {product_id}_ocm_0x{hex_firmware_version}.bin

eg. anx3429_ocm_0x16.bin and the referring analogix ebuild

For all other chips that get added in the future, the recommended PD FW blob name format is: {product_id}_{hardware_version_optional}_0x{hex_firmware_version}.bin

The important thing to note here is that the hexadecimal value of the firmware version is encoded into the firmware blob name.

Uprev ebuild to build the new PD firmware as a package

Once the PD firmware tarball is uploaded to Google Cloud Platform Storage, add an ebuild that builds the new PD firmware as a package. This is just a symlink to the main ebuild package and it just has a different file name - refer to example CL. The PD firmware package name must follow a specific format depending on the TCPC chip type.

For Parade TCPC chips, the format is: parade-{product_id}{hw_version}-firmware-{decimal_fw_version}

eg. parade-ps8751a3-firmware-68

For Analogix TCPC chips, the format is: analogix-{product_id}-firmware-{decimal_fw_version}

eg. analogix-anx3429-firmware-22

In general, the recommended PD firmware package name format is: {vendor_name}-{product_id}{hw_version_optional}-firmware-{decimal_fw_version}

Ebuild uses the decimal value of the firmware version, encoded in the PD firmware package, to identify the package version. The install rules in the ebuild file encodes the firmware version into a separate hash file and strips the same from the firmware blob name.

Note: The PD firmware packages for a new TCPC chip need to be masked by default in the package.mask file. This is usually done when the first PD firmware package for a TCPC chip is added. The required PD firmware version for a board is unmasked in the concerned board's package.unmask file.

Update private overlay of the board to include the new PD firmware

This step is board-specific depending on the requirement to update the PD firmware. The package.unmask file in a board's private overlay is updated to build the new PD firmware version - refer to example CL. This step installs the artifacts of the chosen PD firmware package (i.e. firmware blob & hash files) in the firmware blob path ${SYS_ROOT}/firmware/.

Additionally update the board's private overlay to add the PD firmware artifacts into the CBFS while building coreboot. This is a one time process that needs to be done when the board's private overlay is defined initially - refer to example CL.

Identifying TCPC chips that require firmware update

Depthcharge identifies the TCPC chips that require firmware update by probing the EC. During run-time, depthcharge requests EC for the list of TCPC chips requiring firmware update. Depending on the TCPC configuration, EC responds with the vendor id, product id and the firmware version. Depthcharge uses this information and invokes the appropriate TCPC chip driver to perform the firmware update. To use this approach, enable CONFIG_CROS_EC_PROBE_AUX_FW_INFO in depthcharge - refer to example CL.

Testing PD FW Update

Here are some of the conditions that need to be met for a successful PD firmware update:

Miscellaneous Information

Power-fail safety

PD firmware update tries to recover the TCPC chip in a bad state due to a power cycle during an earlier PD firmware update. At the start of PD firmware update, depthcharge requests the EC for the hard-coded TCPC chip information. Depthcharge uses this informartion to identify the chips requiring PD firmware update. TCPC chips that are in bad state will return the firmware version as 0 leading to a firmware version mismatch. This will cause depthcharge to perform the PD firmware update again.

Identifying PD firmware version on a live/running chip

In order to identify the PD firmware version on a live/running chip, please execute the below command from the Device Under Test (DUT):

ectool pdchipinfo <port_num>

The output of the above command includes the live PD firmware version from the chip. This information can be used to ensure that the PD firmware update is successful.