Re: [PATCH] drm/i915: Disable execlists by default for gen8

From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, stable@vger.linux.kernel
Subject: Re: [PATCH] drm/i915: Disable execlists by default for gen8
Date: Mon, 13 Apr 2015 08:37:37 -0700	[thread overview]
Message-ID: <552BE2C1.80700@virtuousgeek.org> (raw)
In-Reply-To: <1428741697-2137-1-git-send-email-chris@chris-wilson.co.uk>

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@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@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Oscar Mateo <oscar.mateo@intel.com>
> Cc: Damien Lespiau <damien.lespiau@intel.com>
> Cc: Nick Hoath <nicholas.hoath@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Michel Thierry <michel.thierry@intel.com>
> Cc: Arun Siluvery <arun.siluvery@linux.intel.com>
> Cc: John Harrison <John.C.Harrison@Intel.com>
> Cc: Thomas Daniel <thomas.daniel@intel.com>
> Cc: stable@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
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