[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 #52 from Chris Wilson <chris at chris-wilson.co.uk> ---
No, it is just me getting confused between HEAD and START. Ok, I wonder if this
is the missing piece of magic (on top of the current bug branch):

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
b/drivers/gpu/drm/i915/intel_ringbuffer.c
index b46b3e928a7f..12c59e945f8e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -530,15 +530,14 @@ 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)) {
+       if (I915_READ_HEAD(ring)) {
                printk(KERN_ERR
                       "%s initialization failed"
-                      " [%08x != %08x], fudging\n",
+                      " [head now %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);
+                      I915_READ_HEAD(ring));
+               I915_WRITE_HEAD(ring, 0);
+               (void)I915_READ_HEAD(ring);
        }

        iowrite32(MI_NOOP, ring->virtual_start + 0);

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