[Intel-gfx] [PATCH v2] drm/i915: Limit audio CDCLK>=2*BCLK constraint back to GLK only

[Rodrigo Vivi]

On Tue, Dec 31, 2019 at 04:00:07PM +0200, Kai Vehmanen wrote:
> Revert changes done in commit f6ec9483091f ("drm/i915: extend audio
> CDCLK>=2*BCLK constraint to more platforms"). Audio drivers
> communicate with i915 over HDA bus multiple times during system
> boot-up and each of these transactions result in matching
> get_power/put_power calls to i915, and depending on the platform,
> a modeset change causing visible flicker.
> 
> GLK is the only platform with minimum CDCLK significantly lower
> than BCLK, and thus for GLK setting a higher CDCLK is mandatory.
> 
> For other platforms, minimum CDCLK is close but below 2*BCLK
> (e.g. on ICL, CDCLK=176.4kHz with BCLK=96kHz). Spec-wise the constraint
> should be set, but in practise no communication errors have been
> reported and the downside if set is the flicker observed at boot-time.
> 
> Revert to old behaviour until better mechanism to manage
> probe-time clocks is available.
> 
> The full CDCLK>=2*BCLK constraint is still enforced at pipe
> enable time in intel_crtc_compute_min_cdclk().
> 
> Bugzilla: https://gitlab.freedesktop.org/drm/intel/issues/913
> Signed-off-by: Kai Vehmanen <kai.vehmanen at linux.intel.com>
> ---
> 
> Notes:
>     v2: d'oh, change put_power() as well
> 
>  drivers/gpu/drm/i915/display/intel_audio.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_audio.c b/drivers/gpu/drm/i915/display/intel_audio.c
> index 27710098d056..e406719a6716 100644
> --- a/drivers/gpu/drm/i915/display/intel_audio.c
> +++ b/drivers/gpu/drm/i915/display/intel_audio.c
> @@ -856,7 +856,7 @@ static unsigned long i915_audio_component_get_power(struct device *kdev)
>  		}
>  
>  		/* Force CDCLK to 2*BCLK as long as we need audio powered. */
> -		if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
> +		if (IS_GEMINILAKE(dev_priv))

I believe for correctness we should at least say this is for display_10 but
since we don't have display gen defined probably the right thing to do here
is to at least replace this per:

IS_GEN(dev_priv, 10) || IS_GEMINILAKE(dev_priv)

>  			glk_force_audio_cdclk(dev_priv, true);
>  
>  		if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
> @@ -875,7 +875,7 @@ static void i915_audio_component_put_power(struct device *kdev,
>  
>  	/* Stop forcing CDCLK to 2*BCLK if no need for audio to be powered. */
>  	if (--dev_priv->audio_power_refcount == 0)
> -		if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
> +		if (IS_GEMINILAKE(dev_priv))
>  			glk_force_audio_cdclk(dev_priv, false);
>  
>  	intel_display_power_put(dev_priv, POWER_DOMAIN_AUDIO, cookie);
> -- 
> 2.17.1
> 
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