Allwinner VPU support in mainline Linux status update (week 31)

Following on last week’s progress, this week was also focused on bringing the required plumbing for H265 support in our video decoding pipeline. Thanks to register dumps obtained last week from libvdpau-sunxi, it was possible to quickly hack together support for decoding a single intra frame (with no dependency on any other frame), by replaying the dumped register write sequence. Once decoding that single frame worked with the hardcoded register values, we progressively replaced these values with actual register field definitions, that have to be configured with the appropriate metadata for the frame, that is parsed from the H265 bitstream.

As a result, the next step was integrating the required metadata information as dedicated V4L2 controls. Since these controls have to be as generic as possible (in order to fit well with future V4L2 stateless VPU drivers), we carefully looked at the metadata fields that the bitstream offers and considered the elements that VAAPI provides in userspace as well as the information that our VPU needs specifically. It appears that some fields required by our VPU are not exposed by VAAPI directly, so a few tricks were needed along the way.

At this point, we have a first draft for the controls, that allow decoding the intra-coded frame that we dumped last week, but using the metadata provided through the controls instead of hardcoded values :

The very first H265 frame decoded with the Cedrus VPU driver! Can you guess which animation movie it is from?

More work is required to include support for other types of frame coding, namely B and P predictive frames. Next week’s focus will be set on decoding a series of intra-coded frames and moving on to supporting predictive frames. Thankfully, the work done by Bootlin engineer Maxime Ripard when adding support for H264 makes the whole process considerably easier, since H265 resembles H264 in many aspects.

Author: Paul Kocialkowski

Paul is a kernel and embedded Linux engineer at Bootlin, which he joined in 2018. See More details...

2 thoughts on “Allwinner VPU support in mainline Linux status update (week 31)”

  1. Amazing progress, thank you guys for your job!
    I hope that I can get my Pine A64+ from the shelf, which has been gathering dust there for 2 years already 🙂

  2. Hehe also having some shelved aw devices waiting for a new image making it useful.

    Do we need another kickstarter for hdmi audio?! 😉

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