[Bug 76554] [gm45 regression] [drm:init_ring_common]: *ERROR* render ring initialization failed

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=76554

--- Comment #43 from Chris Wilson <chris at chris-wilson.co.uk> ---
If it keeps resetting HEAD to a random value after switching the ring on, how
does it ever work? :|

Another hack:

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 5a74986348c6..e47324aa8963 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -530,6 +530,13 @@ static int init_ring_common(struct intel_ring_buffer
*ring)
                        ((ring->size - PAGE_SIZE) & RING_NR_PAGES)
                        | RING_VALID);

+       if (I915_READ_START(ring) != i915_gem_obj_ggtt_offset(obj)) {
+               printk(KERN_ERR "%s initialization failed [%08x != %08x],
fudging\n",
+                      ring->name, I915_READ_START(ring),
i915_gem_obj_ggtt_offset(obj));
+               I915_WRITE_START(ring, i915_gem_obj_ggtt_offset(obj));
+               POSTING_READ(ring);
+       }
+
        iowrite32(MI_NOOP, ring->virtual_start + 0);
        iowrite32(MI_NOOP, ring->virtual_start + 4);
        ring->write_tail(ring, 8);

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