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

[Jani Nikula]

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")

> 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