[Intel-gfx] [PATCH] drm/i915/audio: fix hdmi audio noise issue

[Yang, Libin]

> -----Original Message-----
> From: Jani Nikula [mailto:jani.nikula at linux.intel.com]
> Sent: Wednesday, November 9, 2016 6:59 PM
> To: Yang, Libin <libin.yang at intel.com>; intel-gfx at lists.freedesktop.org;
> ville.syrjala at linux.intel.com; Vetter, Daniel <daniel.vetter at intel.com>;
> tiwai at suse.de
> Cc: Yang, Libin <libin.yang at intel.com>
> Subject: Re: [PATCH] drm/i915/audio: fix hdmi audio noise issue
> 
> On Wed, 09 Nov 2016, libin.yang at intel.com wrote:
> > From: Libin Yang <libin.yang at intel.com>
> >
> > This issue is caused by:
> > 6014ac12: drm/i915/audio: set proper N/M in modeset
> >
> > Some special monitors will have noise or even no sound after applying
> > the patch 6014ac12.
> >
> > In patch 6014ac12, it will reset the cts value to 0 for HDMI.
> > However, we need disable Enable CTS or M Prog bit. This is the initial
> > setting after HW reset.
> >
> 
> Fixes: 6014ac122ed0 ("drm/i915/audio: set proper N/M in modeset")

Get it. Thanks.

> 
> > Signed-off-by: Libin Yang <libin.yang at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_audio.c | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_audio.c
> > b/drivers/gpu/drm/i915/intel_audio.c
> > index 813fd74..a472d35 100644
> > --- a/drivers/gpu/drm/i915/intel_audio.c
> > +++ b/drivers/gpu/drm/i915/intel_audio.c
> > @@ -332,6 +332,13 @@ hsw_hdmi_audio_config_update(struct intel_crtc
> *intel_crtc, enum port port,
> >  	int n;
> >  	u32 tmp;
> >
> > +	/* reset CTS value to 0 */
> > +	tmp = I915_READ(HSW_AUD_M_CTS_ENABLE(pipe));
> > +	tmp &= ~AUD_CONFIG_M_MASK;
> > +	tmp &= ~AUD_M_CTS_M_VALUE_INDEX;
> > +	tmp |= AUD_M_CTS_M_PROG_ENABLE;
> > +	I915_WRITE(HSW_AUD_M_CTS_ENABLE(pipe), tmp);
> > +
> >  	tmp = I915_READ(HSW_AUD_CFG(pipe));
> >  	tmp &= ~AUD_CONFIG_N_VALUE_INDEX;
> >  	tmp &= ~AUD_CONFIG_PIXEL_CLOCK_HDMI_MASK;
> > @@ -351,10 +358,12 @@ hsw_hdmi_audio_config_update(struct intel_crtc
> > *intel_crtc, enum port port,
> >
> >  	I915_WRITE(HSW_AUD_CFG(pipe), tmp);
> >
> > +	/*
> > +	 * Let's disable "Enable CTS or M Prog bit"
> > +	 * and let HW calculate the value
> > +	 */
> >  	tmp = I915_READ(HSW_AUD_M_CTS_ENABLE(pipe));
> > -	tmp &= ~AUD_CONFIG_M_MASK;
> > -	tmp &= ~AUD_M_CTS_M_VALUE_INDEX;
> > -	tmp |= AUD_M_CTS_M_PROG_ENABLE;
> > +	tmp &= ~AUD_M_CTS_M_PROG_ENABLE;
> >  	I915_WRITE(HSW_AUD_M_CTS_ENABLE(pipe), tmp);
> 
> Is it necessary to do the HSW_AUD_M_CTS_ENABLE updates in two places?
> Why do you both enable and disable AUD_M_CTS_M_PROG_ENABLE bit here?
> 
> BR,
> Jani.
> 
> 
> >  }
> 
> --
> Jani Nikula, Intel Open Source Technology Center