[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 #45 from Jiri Kosina <jikos at jikos.cz> ---
(In reply to comment #44)
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 5a74986348c6..b46b3e928a7f 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -530,6 +530,17 @@ 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);

What is a baseline I should apply this on top of, please? The surrounding code
in my tree (with all the patches provided so far apples) is

[ ... ]
        I915_WRITE_CTL(ring,
                        ((ring->size - PAGE_SIZE) & RING_NR_PAGES)
                        | RING_VALID);
        if (wait_for(I915_READ_CTL(ring) & RING_VALID, 1000)) {
                DRM_ERROR("%s initialization failed ctl %08x (valid? %d)\n",
                                ring->name,
                                I915_READ_CTL(ring),
                                !!(I915_READ_CTL(ring) & RING_VALID));
                ret = -EIO;
                goto out;
        }
        I915_WRITE_HEAD(ring, 0);
        ring->write_tail(ring, 0);

        iowrite32(MI_NOOP, ring->virtual_start + 0);
        iowrite32(MI_NOOP, ring->virtual_start + 4);
        ring->write_tail(ring, 8);
[ ... ]

(i.e. it has the extra I915_WRITE_HEAD(ring, 0); ring->write_tail(ring, 0);,
etc).

I can of course easily apply the hunk just between the 

   ring->write_tail(ring, 0);

and 

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

if that's what you want me to do.

Thanks.

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