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Date:	Thu, 7 Aug 2014 16:36:49 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Pavel Machek <pavel@....cz>,
	Linux-pm mailing list <linux-pm@...ts.osdl.org>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [Intel-gfx] 3.15-rc: regression in suspend

On Thu, Aug 07, 2014 at 02:47:21PM +0200, Jiri Kosina wrote:
> On Fri, 11 Jul 2014, Pavel Machek wrote:
> 
> > > > > Ok, so I have set up machines for ktest / autobisect, and found out that 
> > > > > 3.16-rc1 no longer has that problem. Oh well, bisect would not be fun, 
> > > > > anyway...
> > > > 
> > > > I am still seeing the problem with 3.16-rc2.
> > > 
> > > I'm confused now. Is the bisect result
> > > 
> > > commit 773875bfb6737982903c42d1ee88cf60af80089c
> > > Author: Daniel Vetter <daniel.vetter@...ll.ch>
> > > Date:   Mon Jan 27 10:00:30 2014 +0100
> > > 
> > >     drm/i915: Don't set the 8to6 dither flag when not scaling
> > > 
> > > now the culprit or not? Or do we have 2 different bugs at hand here?
> > 
> > Three different issues, it seems. Two ring initialization problems,
> > one went away in 3.16 (for me), second did not (suspend for jikos),
> > third -- trivial issue with 8to6 dither.
> 
> The patch below seems to finally cure the problem at my system; I've just 
> attached it to freedesktop bugzilla, but sending it to this thread as well 
> to hopefully get as much testing coverage by affected people as possible.
> 
> I am going on with testing whether it really completely fixes the problem 
> or just made it less likely.

Picked up for -fixes, thanks for the patch.
-Daniel
> 
> 
> 
> 
> 
> From: Jiri Kosina <jkosina@...e.cz>
> Subject: [PATCH] drm/i915: read HEAD register back in init_ring_common() to enforce ordering
> 
> Withtout this, ring initialization fails reliabily during resume with
> 
> 	[drm:init_ring_common] *ERROR* render ring initialization failed ctl 0001f001 head ffffff8804 tail 00000000 start 000e4000
> 
> Signed-off-by: Jiri Kosina <jkosina@...e.cz>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 279488a..7add7ee 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -517,6 +517,9 @@ static int init_ring_common(struct intel_engine_cs *ring)
>  	else
>  		ring_setup_phys_status_page(ring);
>  
> +	/* Enforce ordering by reading HEAD register back */
> +	I915_READ_HEAD(ring);
> +
>  	/* Initialize the ring. This must happen _after_ we've cleared the ring
>  	 * registers with the above sequence (the readback of the HEAD registers
>  	 * also enforces ordering), otherwise the hw might lose the new ring
> 
> -- 
> Jiri Kosina
> SUSE Labs
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@...ts.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
--
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