[Intel-gfx] [PATCH] drm/i915: Disable execlists by default for gen8

[Jesse Barnes]

On 04/11/2015 01:41 AM, Chris Wilson wrote:
> Bug reports are still coming in for late 4.0-rcX that indicate that
> execlists causes GPU hangs following resume.
> 
> Fixes regression from
> commit d7f621e50704306c348ccb192f17047f1499f9bc
> Author: Oscar Mateo <oscar.mateo at intel.com>
> Date:   Thu Jul 24 17:04:49 2014 +0100
> 
>     drm/i915/bdw: Enable Logical Ring Contexts (hence, Execlists)
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89308
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Oscar Mateo <oscar.mateo at intel.com>
> Cc: Damien Lespiau <damien.lespiau at intel.com>
> Cc: Nick Hoath <nicholas.hoath at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Michel Thierry <michel.thierry at intel.com>
> Cc: Arun Siluvery <arun.siluvery at linux.intel.com>
> Cc: John Harrison <John.C.Harrison at Intel.com>
> Cc: Thomas Daniel <thomas.daniel at intel.com>
> Cc: stable at vger.linux.kernel
> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index a3ad95b6ea51..1b289481a9b3 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -232,9 +232,15 @@ int intel_sanitize_enable_execlists(struct drm_device *dev, int enable_execlists
>  	if (enable_execlists == 0)
>  		return 0;
>  
> +#if 0
> +	/* Disable execlists by default for 4.0, since we still have
> +	 * issues upon resume in the wild, e.g.
> +	 * https://bugs.freedesktop.org/show_bug.cgi?id=89308
> +	 */
>  	if (HAS_LOGICAL_RING_CONTEXTS(dev) && USES_PPGTT(dev) &&
>  	    i915.use_mmio_flip >= 0)
>  		return 1;
> +#endif
>  
>  	return 0;
>  }
> 

But disabling execlists introduces its own problems, right?  Or was that
just with semaphores enabled, which we don't have right now?

Either way, we should root cause this one since it may be hiding on
gen9+ too...  any takers?

Jesse