On Tue, Apr 12, 2016 at 09:03:06PM +0100, Chris Wilson wrote:
> For reasons unknown Sandybridge GT1 (at least) will eventually hang when
> it encounters a ring wraparound at offset 0. The test case that
> reproduces the bug reliably forces a large number of interrupted context
> switches, thereby causing very frequent ring wraparounds, but there are
> similar bug reports in the wild with the same symptoms, seqno writes
> stop just before the wrap and the ringbuffer at address 0. It is also
> timing crucial, but adding various delays hasn't helped pinpoint where
> the window lies.
>
> Whether the fault is restricted to the ringbuffer itself or the GTT
> addressing is unclear, but moving the ringbuffer fixes all the hangs I
> have been able to reproduce.
>
> References: (e.g.) https://bugs.freedesktop.org/show_bug.cgi?id=93262
> Testcase: igt/gem_exec_whisper/render-contexts-interruptible #snb-gt1
> Signed-off-by: Chris Wilson
> Cc: sta...@vger.kernel.org
Acked-by: Daniel Vetter
> ---
> drivers/gpu/drm/i915/intel_ringbuffer.c | 7 +--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 8391382431b2..904a8a276f6a 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -2096,10 +2096,12 @@ int intel_pin_and_map_ringbuffer_obj(struct
> drm_device *dev,
> struct drm_i915_private *dev_priv = to_i915(dev);
> struct i915_ggtt *ggtt = &dev_priv->ggtt;
> struct drm_i915_gem_object *obj = ringbuf->obj;
> + /* Ring wraparound at offset 0 sometimes hangs. No idea why. */
> + unsigned flags = PIN_OFFSET_BIAS | 4096;
> int ret;
>
> if (HAS_LLC(dev_priv) && !obj->stolen) {
> - ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, 0);
> + ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, flags);
> if (ret)
> return ret;
>
> @@ -2113,7 +2115,8 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device
> *dev,
> goto err_unpin;
> }
> } else {
> - ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE, PIN_MAPPABLE);
> + ret = i915_gem_obj_ggtt_pin(obj, PAGE_SIZE,
> + flags | PIN_MAPPABLE);
> if (ret)
> return ret;
>
> --
> 2.8.0.rc3
>
> ___
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> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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