Allwinner VPU support in mainline Linux status update (week 20)

With DMABUF support tested, it has become possible for Paul to start the work on integrating a GPU-based video output pipeline with Sunxi-Cedrus. Using the GPU should greatly improve performance when it comes to displaying the video frames. As of now, we have been using software untiling, software YUV-to-RGB colorspace conversion and software scaling. We are looking to replace these steps with GPU-based untiling, colorspace conversion and scaling. Shaders are used to implement these operations: they are small programs that are compiled on-the-fly for the GPU’s very specialized instruction set. Most players embed shaders (in their source form, using the GL shading language) for usual operations like colorspace conversion and scaling. However, these players are not ready to handle untiling as of now (or even be notified that the format returned by our VAAPI backend is tiled).

The first step in our plan is to get VLC to cooperate with the X11 flavor of the Mali proprietary blobs that Allwinner has released in the past so that we can use GPU support for colorspace and scaling. This is still a blocking point as of now. Then, we will look into crafting a shader for untiling the VPU output frame and integrating it with our libva-cedrus VAAPI backend.

As a sidenote, the free software Lima driver is being prepared for a first RFC series, bringing the first bits of mainline Linux kernel support for Mali GPUs of the Utgard generation. So even though work on the GPU only concerns the proprietary blob for now, the work will eventually become useful to the free software driver as well.

We have also tested Sunxi-Cedrus on the H3 and started looking at integrating the display part (which differs from earlier SoCs by using a revised display engine: DE2). However, since this is a strech goal of the fundraiser and that we have many other tasks left to tack among our main goals, this is by far not our priority at the moment.

We finally worked more on the libva-dump and cedrus-frame-test for H264, which will hopefully allow us to test our first H264 decoding next week!

Stay tuned for our next progress update!

Author: Paul Kocialkowski

Paul is a kernel and embedded Linux intern at Bootlin. You can find more details about Paul on his personal website: http://www.paulk.fr/

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