[Intel-gfx] [CI-ping 12/15] drm/i915: Force ringbuffers to not be at offset 0

[Daniel Vetter]

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 <chris at chris-wilson.co.uk>
> Cc: stable at vger.kernel.org

Acked-by: Daniel Vetter <daniel.vetter at ffwll.ch>

> ---
>  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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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch