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

[Ville Syrjälä]

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?

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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-- 
Ville Syrjälä
Intel OTC