Merged back in 2023 was Intel ANV Vulkan Video support for H.265 decoding. But it's been slightly out of compliant with the Vulkan spec, which is now fixed with the newest code for Mesa 26.3 by engaging the HuC firmware.

Hyunjun Ko of Igalia has been leading much of the work around Intel ANV Vulkan Video support in Mesa with Intel engineers principally focused on the Video Acceleration API (VA-API) for the video acceleration needs of their customers. Ko recently landed H.265 10-bit encode and AV1 encode for DG2/Alchemist while now he's gone back and improved the H.265 decoding.

The H.265 decoding is now dependent upon the Intel HuC micro-controller firmware being loaded so its bitstream parsing doesn't end up violating the Vulkan spec. He explained in the merge request:

"Previously, we've been parsing the bitstream on the CPU at record time, which would violate the Vulkan spec as the application is allowed to fill the buffer after recording.

To fix this, we emit the HuC S2L (short-to-long) sequence. The S2L firmware kernel parses the HEVC slice headers from the bitstream buffer on the GPU at execution time and writes the corresponding HCP slice commands into second-level batch buffer.

Also we probe via I915_PARAM_HUC_STATUS to confirm the HuC is loaded and decide to enable/disable h265 decoding."

Most users end up having the HuC firmware loaded on their system alongside the GuC, so in practice it shouldn't add any burden while ensuring that the Vulkan Video H.265 decoding aligns with the spec. The HuC is used for media processing offload and dates back all the way to their Gen9 graphics where it was originally introduced.

This code was merged today for next quarter's Mesa 26.3 feature release.