Module Name: src
Committed By: riastradh
Date: Wed Feb 25 13:30:02 UTC 2015
Modified Files:
src/sys/external/bsd/drm2/dist/drm/i915: intel_ringbuffer.c
Log Message:
Back-port attempt [1/2] to fix i915drmkms on G4X, from Linux.
commit ece4a17d237a79f63fbfaf3f724a12b6d500555c
Author: Jiri Kosina <jkos...@suse.cz>
Date: Thu Aug 7 16:29:53 2014 +0200
drm/i915: read HEAD register back in init_ring_common() to enforce ordering
Withtout this, ring initialization fails reliabily during resume with
[drm:init_ring_common] *ERROR* render ring initialization failed ctl 000
1f001 head ffffff8804 tail 00000000 start 000e4000
This is not a complete fix, but it is verified to make the ring
initialization failures during resume much less likely.
We were not able to root-cause this bug (likely HW-specific to Gen4 chips)
yet. This is therefore used as a ducttape before problem is fully
understood and proper fix created, so that people don't suffer from
completely unusable systems in the meantime.
The discussion and debugging is happening at
https://bugs.freedesktop.org/show_bug.cgi?id=76554
To generate a diff of this commit:
cvs rdiff -u -r1.4 -r1.5 \
src/sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c
diff -u src/sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c:1.4 src/sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c:1.5
--- src/sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c:1.4 Wed Jul 16 20:56:25 2014
+++ src/sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c Wed Feb 25 13:30:02 2015
@@ -499,6 +499,9 @@ static int init_ring_common(struct intel
else
ring_setup_phys_status_page(ring);
+ /* Enforce ordering by reading HEAD register back */
+ I915_READ_HEAD(ring);
+
/* Initialize the ring. This must happen _after_ we've cleared the ring
* registers with the above sequence (the readback of the HEAD registers
* also enforces ordering), otherwise the hw might lose the new ring
