[src/trunk]: src/sys/external/bsd/drm2/dist/drm/i915 Back-port attempt [2/2] ...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/23cf51895059
branches:  trunk
changeset: 336308:23cf51895059
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Wed Feb 25 13:35:25 2015 +0000

description:
Back-port attempt [2/2] to fix i915drmkms on G4X, from Linux.

commit 95468892fdfeef6d1004b524e35957629efdbe00
Author: Chris Wilson <chris%chris-wilson.co.uk@localhost>
Date:   Thu Aug 7 15:39:54 2014 +0100

    drm/i915: Reset the HEAD pointer for the ring after writing START

    Ville found an old w/a documented for g4x that suggested that we need to
    reset the HEAD after writing START. This is a useful fixup for some of
    the g4x ring initialisation woes, but as usual, not all.

    v2: Do the rewrite unconditionally anyway

diffstat:

 sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c |  8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diffs (18 lines):

diff -r 4345f289eefb -r 23cf51895059 sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c
--- a/sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c    Wed Feb 25 13:30:02 2015 +0000
+++ b/sys/external/bsd/drm2/dist/drm/i915/intel_ringbuffer.c    Wed Feb 25 13:35:25 2015 +0000
@@ -507,6 +507,14 @@
         * also enforces ordering), otherwise the hw might lose the new ring
         * register values. */
        I915_WRITE_START(ring, i915_gem_obj_ggtt_offset(obj));
+
+       /* WaClearRingBufHeadRegAtInit:ctg,elk */
+       if (I915_READ_HEAD(ring))
+               DRM_DEBUG("%s initialization failed [head=%08x], fudging\n",
+                         ring->name, I915_READ_HEAD(ring));
+       I915_WRITE_HEAD(ring, 0);
+       (void)I915_READ_HEAD(ring);
+
        I915_WRITE_CTL(ring,
                        ((ring->size - PAGE_SIZE) & RING_NR_PAGES)
                        | RING_VALID);