Allwinner VPU support in mainline Linux status update (week 21)

This week’s effort was focused on getting VLC to accelerate its video output using the Mali proprietary blobs. More specifically, two distinct interfaces are involved: EGL, that allows interacting with the platform’s windowing system (in our case, X11) and GLES, that is in charge of the rendering operations. While VLC already had support for both of these interfaces, it initially failed to create and use its GL-backed video output module with the Mali GPU blobs. Although everything indicated that it should have been working, the GLES calls were failing while EGL was setup and behaving correctly. The issue at hand was directly related to VLC using Qt for its interface. Because the Qt build used on the development boards was targeting GL support instead of GLES, it needed to import GL symbols that have the same name as GLES equivalents. Since Qt was loaded after the video output module, it would override the matching GLES symbols with GL symbols (from Mesa, not the blob).

With the help of Thomas Guillem, a few patches were crafted to fix the issue and sent out to the VLC developers. Some more revisions of these patches will be needed for the fix to integrate the VLC tree, but it should land sooner or later.

With VLC fixed, it was time to start looking at accelerating our pipeline with the GPU. VLC already includes GPU shaders for NV12 to RGB conversion as well as scaling and rotation, but does not have support for our tiled format. This is why we need a shader on our VAAPI backend side to accelerate the untiling operation. While the shader is currently work in progress, further work is also required to properly export the resulting untiled buffer as a DMABUF handle for VLC. Since the GPU blob does not support dmabuf export, we will need to implement a standalone GBM provider compatible with our DRM driver, that will handle allocating surfaces (instead of the armsoc DDX that is currently used for accelerated graphics on X) and exporting DMABUF handles to them when needed. Generally speaking, this will also allow standardizing and sanitizing the integration of the Mali blobs with the rest of the system.

Stay tuned for our next 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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