[PATCH 0/2] drm/radeon: fix VCE1 encoding on SI by handling the VCE interrupt

[Matheus Tagliari <mptagliari@gmail.com>]

Hardware H.264 encoding with the VCE block on SI GPUs (radeon driver)
hangs the GPU after a few dozen frames.  I hit it with the KDE Plasma
RDP server, which encodes through VAAPI, and reproduced it with a
plain "ffmpeg -vaapi_device ... -c:v h264_vaapi" test on a Radeon HD
8870M (Cape Verde).

The VCE1 code never enables the VCE trap interrupt and the SI (and
Trinity) interrupt handlers do not process it, unlike the CIK code and
amdgpu.  Patch 1 adds the handlers, patch 2 enables the interrupt.

Results on Debian 6.12.113 (see patch 2 for numbers): hang before,
none after, and 34 fps instead of ~4 fps for the workaround that avoids
the hang.  The KDE RDP server (KRDP) itself, driven by a local FreeRDP
client, now encodes on the VCE ring for several minutes (about 40
fences per second on ring 6 in the radeon_fence_emit tracepoint) with a
clean kernel log.

Two caveats:

 - I have not worked out why the missing interrupt turns into ring
   lockups instead of only added latency.  What I know is that the
   hang needs the VCE ring to wait on a hardware semaphore (disabling
   only the waiting side, or both sides, of radeon_vce_semaphore_emit()
   avoids it) and that handling the interrupt makes it go away with
   the semaphores left enabled.  If someone knows why, I would be glad
   to improve the commit message.
 - The Trinity/Richland change is compile tested only.

The series was developed and tested on Debian's 6.12.113 with the
radeon module built out of tree.  It applies cleanly on drm-next
(fad06cf), where drivers/gpu/drm/radeon builds without warnings (W=1,
allmodconfig) both after patch 1 and with the whole series.

Matheus Tagliari (2):
  drm/radeon: process the VCE interrupt on SI and Trinity
  drm/radeon/vce1: enable the VCE trap interrupt

 drivers/gpu/drm/radeon/evergreen.c | 14 ++++++++++++++
 drivers/gpu/drm/radeon/si.c        | 14 ++++++++++++++
 drivers/gpu/drm/radeon/sid.h       |  2 ++
 drivers/gpu/drm/radeon/vce_v1_0.c  |  4 ++++
 4 files changed, 34 insertions(+)


base-commit: fad06cfaf385787b9ffa2f73f049d42dbe1de57f
-- 
2.47.3