Re: [PATCH v2] drm/i915/audio: fix hdmi audio noise issue

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 11 Nov 2016, "Yang, Libin" <libin.yang@intel.com> wrote:
> Hi Jani,
>
>> -----Original Message-----
>> From: Jani Nikula [mailto:jani.nikula@linux.intel.com]
>> Sent: Thursday, November 10, 2016 6:37 PM
>> To: Yang, Libin <libin.yang@intel.com>; intel-gfx@lists.freedesktop.org;
>> ville.syrjala@linux.intel.com; Vetter, Daniel <daniel.vetter@intel.com>;
>> tiwai@suse.de
>> Cc: Yang, Libin <libin.yang@intel.com>
>> Subject: Re: [PATCH v2] drm/i915/audio: fix hdmi audio noise issue
>> 
>> On Thu, 10 Nov 2016, libin.yang@intel.com wrote:
>> > From: Libin Yang <libin.yang@intel.com>
>> >
>> > Some 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 to 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")
>> > Signed-off-by: Libin Yang <libin.yang@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);
>> 
>> You did not address my review comment on the earlier version:
>> 
>> 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?
>
> Sorry, I missed your comments.
>
> The first doing the HSW_AUD_M_CTS_ENABLE is to reset the M value to 0.
> The second doing the HSW_AUD_M_CTS_ENABLE is to let HW calculate the M value.
>
> Or we can just try to disable the HSW_AUD_M_CTS_ENABLE bit. What's your opinion?

I would have thought just doing the latter would be sufficient. Please
test.

BR,
Jani.

>
> Regards,
> Libin
>
>> 
>> BR,
>> Jani.
>> 
>> 
>> >  }
>> 
>> --
>> Jani Nikula, Intel Open Source Technology Center

-- 
Jani Nikula, Intel Open Source Technology Center
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