re: amdgpu progress

unfortunately, new mesa regressees a problem i've had with amdgpu
going back a while now that no longer occurs with mesa 19 and xsrc.
(i was running with your os_file.c change as well.)

i had an old test - run several glxgears at the same time, with
non-overlapping windows, and then play a video with mpv.

in the last couple of months, xsrc with mesa 19 started working
for me and this problem.  i had tested earlier this year and it
was still broken.  i can't reproduce this issue with -current
and -current xsrc, but it appears again easily with -current src
and current pkgsrc.  the mpv hangs, amdgpu in the kernel does a
reset cycle that doesn't work.  see this for my original report
about the reste failing:

   https://github.com/riastradh/netbsd-src/issues/28

and this for the what happens after glxgears + mpv run:

   https://github.com/riastradh/netbsd-src/issues/24

both i recently found was no longer a problem... i thought.

not sure what is going on here.

the pkgsrc amdgpu issue is odd.  the amdgpu xf86 driver should
be telling mesa to load "radeonsi", and this seems to work with
xsrc:

xf86-video-amdgpu/dist/src/amdgpu_version.h:39:#define SI_DRIVER_NAME       "radeonsi"
xf86-video-amdgpu/dist/src/amdgpu_dri2.c:1308:      dri2_info.driverName = SI_DRIVER_NAME;


i don't claim to understand all of this.


.mrg.

(fwiw, mesa 21 in xsrc with radeon seems good, though i have
only tested so far with an older amd laptop apu.)