2017-10-10: VC5 GPU reset, VC5 GL, DSI panel

I spent this week in front of the VC5 hardware, working toward implementing GPU reset. I’m going to need reliable reset before I can start running GL testsuites.

Of course, to believe that GPU reset works, I’m going to want some tests that trigger it. I pulled the VC5 XML-based code-generation from Mesa into i-g-t, and built up basic rendering tests using it. It caught that I was misusing struct scatterlist (causing CPU page faults trying to fill the VC5 MMU). I also had mistyped a bit of the XML, calling a bitmask a bool so that the hardware tried to store render targets 1, 2, and 3, instead of 0 (causing GPU hangs). After stabilizing all that, building the hang testcase was pretty simple.

Taking a break from kernel adventures, I did a bit more work on the vc5 GL driver. Transform feedback now has many tests passing, provoking vertex is supported, float32 render targets are supported, MRTs are supported, colormasks are fixed for non-independent blending, a regression in blending with a 0 factor is fixed, and >32bpp clear colors are fixed.

I’ve got a new revision of Boris’s VC4 MADVISE work, and it’s looking good. Boris has also cleaned up some debug messages that have been spamming dmesg on the Raspberry Pi, which is great news for us.

I also spent quite some time reviewing Dylan’s meson work for Mesa. It’s a slog – build systems for a project of Mesa’s scale are huge, but I’ve seen what meson can get you in productivity gains from my conversion of the X Server, and it looks like we should be able to replace all 3(!) of Mesa’s build systems with this one.

Finally, on Friday I got the reviews necessary for the DSI panel driver, and I merged it to drm-misc-next to appear in the 4.15 kernel. We still need to figure out what to do about the devicetree for it (since it’s sort of an optional piece of hardware for the board, but more official than other hardware), but at least this is a lot less for downstreams to carry.

Next week: merging vc5 GL and working on actually performing GPU reset.