[PATCH] drm/i915/ilk: Wait one vblank before enabling audio

[Lyude Paul]

On Mon, 2016-05-23 at 21:06 +0300, Ville Syrjälä wrote:
> On Fri, May 20, 2016 at 05:36:40PM -0400, Lyude wrote:
> > 
> > We no longer call ilk_audio_codec_enable() while we have vblanks
> > disabled. As such, we can finally fix this and stop the occasional pipe
> > underruns I'm seeing on this Dell OptiPlex 990.
> Hmm. Are you still getting underruns on -nightly?
For me the problem isn't just underruns, a lot of times the modeset results in a
blank monitor without this fix… afaict waiting for 1 vblank seems to fix the
issue entirely here, but I'll check more thoroughly in a bit and update you if I
manage to get it to underrun.

Cheers,
Lyude

> 
> I basically tried this same thing (+ a bunch of other tweaks to the
> audio enable sequence) when I was hunting the remaining underruns on
> my ILK, but in the end audio was a red herring. So I never found
> any real benefit from extra vblank waits in the audio enable sequence.
> They did appear to help sometimes, but with a enough repetitions it
> still failed.
> 
> > 
> > 
> > Cc: stable at vger.kernel.org
> > Signed-off-by: Lyude <cpaul at redhat.com>
> > ---
> >  drivers/gpu/drm/i915/intel_audio.c | 8 ++------
> >  1 file changed, 2 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_audio.c
> > b/drivers/gpu/drm/i915/intel_audio.c
> > index 7d281b4..0d685fe 100644
> > --- a/drivers/gpu/drm/i915/intel_audio.c
> > +++ b/drivers/gpu/drm/i915/intel_audio.c
> > @@ -423,12 +423,8 @@ static void ilk_audio_codec_enable(struct drm_connector
> > *connector,
> >  	if (WARN_ON(port == PORT_A))
> >  		return;
> >  
> > -	/*
> > -	 * FIXME: We're supposed to wait for vblank here, but we have
> > vblanks
> > -	 * disabled during the mode set. The proper fix would be to push
> > the
> > -	 * rest of the setup into a vblank work item, queued here, but the
> > -	 * infrastructure is not there yet.
> > -	 */
> > +	/* Need to wait one vblank before enabling audio */
> > +	intel_wait_for_vblank(connector->dev, pipe);
> >  
> >  	if (HAS_PCH_IBX(connector->dev)) {
> >  		hdmiw_hdmiedid = IBX_HDMIW_HDMIEDID(pipe);
> > -- 
> > 2.5.5
> > 
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