Re: [PATCH 1/8] drm/i915: Skip modifying PCH DREF if not changing clock sources

[Imre Deak <imre.deak@intel.com>]

On Wed, 2013-02-06 at 11:10 +0000, Chris Wilson wrote:
> Modifying the clock sources (via the DREF control on the PCH) is a slow
> multi-stage process as we need to let the clocks stabilise between each
> stage. If we are not actually changing the clock sources, then we can
> return early.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_display.c |   83 +++++++++++++++++++++++++---------
>  1 file changed, 61 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index d75c6a0..f1dbd01 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -4749,7 +4749,7 @@ static void ironlake_init_pch_refclk(struct drm_device *dev)
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct drm_mode_config *mode_config = &dev->mode_config;
>  	struct intel_encoder *encoder;
> -	u32 temp;
> +	u32 val, final;
>  	bool has_lvds = false;
>  	bool has_cpu_edp = false;
>  	bool has_pch_edp = false;
> @@ -4792,70 +4792,109 @@ static void ironlake_init_pch_refclk(struct drm_device *dev)
>  	 * PCH B stepping, previous chipset stepping should be
>  	 * ignoring this setting.
>  	 */
> -	temp = I915_READ(PCH_DREF_CONTROL);
> +	val = I915_READ(PCH_DREF_CONTROL);
> +
> +	/* As we must carefully and slowly disable/enable each source in turn,
> +	 * compute the final state we want first and check if we need to
> +	 * make any changes at all.
> +	 */
> +	final = val;
> +	final &= ~DREF_NONSPREAD_SOURCE_MASK;
> +	if (has_ck505)
> +		final |= DREF_NONSPREAD_CK505_ENABLE;
> +	else
> +		final |= DREF_NONSPREAD_SOURCE_ENABLE;
> +
> +	final &= ~DREF_SSC_SOURCE_MASK;
> +	final &= ~DREF_CPU_SOURCE_OUTPUT_MASK;
> +	final &= ~DREF_SSC1_ENABLE;
> +
> +	if (has_panel) {
> +		final |= DREF_SSC_SOURCE_ENABLE;
> +
> +		if (intel_panel_use_ssc(dev_priv) && can_ssc)
> +			final |= DREF_SSC1_ENABLE;
> +
> +		if (has_cpu_edp) {
> +			if (intel_panel_use_ssc(dev_priv) && can_ssc)
> +				final |= DREF_CPU_SOURCE_OUTPUT_DOWNSPREAD;
> +			else
> +				final |= DREF_CPU_SOURCE_OUTPUT_NONSPREAD;
> +		} else
> +			final |= DREF_CPU_SOURCE_OUTPUT_DISABLE;
> +	} else {
> +		final |= DREF_SSC_SOURCE_DISABLE;
> +		final |= DREF_CPU_SOURCE_OUTPUT_DISABLE;
> +	}
> +
> +	if (final == val)
> +		return;
> +

Nitpick: this would be clearer in a seperate function with a
'check_only' param, then the below could be removed.

>  	/* Always enable nonspread source */
> -	temp &= ~DREF_NONSPREAD_SOURCE_MASK;
> +	val &= ~DREF_NONSPREAD_SOURCE_MASK;
>  
>  	if (has_ck505)
> -		temp |= DREF_NONSPREAD_CK505_ENABLE;
> +		val |= DREF_NONSPREAD_CK505_ENABLE;
>  	else
> -		temp |= DREF_NONSPREAD_SOURCE_ENABLE;
> +		val |= DREF_NONSPREAD_SOURCE_ENABLE;
>  
>  	if (has_panel) {
> -		temp &= ~DREF_SSC_SOURCE_MASK;
> -		temp |= DREF_SSC_SOURCE_ENABLE;
> +		val &= ~DREF_SSC_SOURCE_MASK;
> +		val |= DREF_SSC_SOURCE_ENABLE;
>  
>  		/* SSC must be turned on before enabling the CPU output  */
>  		if (intel_panel_use_ssc(dev_priv) && can_ssc) {
>  			DRM_DEBUG_KMS("Using SSC on panel\n");
> -			temp |= DREF_SSC1_ENABLE;
> +			val |= DREF_SSC1_ENABLE;
>  		} else
> -			temp &= ~DREF_SSC1_ENABLE;
> +			val &= ~DREF_SSC1_ENABLE;
>  
>  		/* Get SSC going before enabling the outputs */
> -		I915_WRITE(PCH_DREF_CONTROL, temp);
> +		I915_WRITE(PCH_DREF_CONTROL, val);
>  		POSTING_READ(PCH_DREF_CONTROL);
>  		udelay(200);
>  
> -		temp &= ~DREF_CPU_SOURCE_OUTPUT_MASK;
> +		val &= ~DREF_CPU_SOURCE_OUTPUT_MASK;
>  
>  		/* Enable CPU source on CPU attached eDP */
>  		if (has_cpu_edp) {
>  			if (intel_panel_use_ssc(dev_priv) && can_ssc) {
>  				DRM_DEBUG_KMS("Using SSC on eDP\n");
> -				temp |= DREF_CPU_SOURCE_OUTPUT_DOWNSPREAD;
> +				val |= DREF_CPU_SOURCE_OUTPUT_DOWNSPREAD;
>  			}
>  			else
> -				temp |= DREF_CPU_SOURCE_OUTPUT_NONSPREAD;
> +				val |= DREF_CPU_SOURCE_OUTPUT_NONSPREAD;
>  		} else
> -			temp |= DREF_CPU_SOURCE_OUTPUT_DISABLE;
> +			val |= DREF_CPU_SOURCE_OUTPUT_DISABLE;
>  
> -		I915_WRITE(PCH_DREF_CONTROL, temp);
> +		I915_WRITE(PCH_DREF_CONTROL, val);
>  		POSTING_READ(PCH_DREF_CONTROL);
>  		udelay(200);
>  	} else {
>  		DRM_DEBUG_KMS("Disabling SSC entirely\n");
>  
> -		temp &= ~DREF_CPU_SOURCE_OUTPUT_MASK;
> +		val &= ~DREF_CPU_SOURCE_OUTPUT_MASK;
>  
>  		/* Turn off CPU output */
> -		temp |= DREF_CPU_SOURCE_OUTPUT_DISABLE;
> +		val |= DREF_CPU_SOURCE_OUTPUT_DISABLE;
>  
> -		I915_WRITE(PCH_DREF_CONTROL, temp);
> +		I915_WRITE(PCH_DREF_CONTROL, val);
>  		POSTING_READ(PCH_DREF_CONTROL);
>  		udelay(200);
>  
>  		/* Turn off the SSC source */
> -		temp &= ~DREF_SSC_SOURCE_MASK;
> -		temp |= DREF_SSC_SOURCE_DISABLE;
> +		val &= ~DREF_SSC_SOURCE_MASK;
> +		val |= DREF_SSC_SOURCE_DISABLE;
>  
>  		/* Turn off SSC1 */
> -		temp &= ~ DREF_SSC1_ENABLE;
> +		val &= ~ DREF_SSC1_ENABLE;
>  
> -		I915_WRITE(PCH_DREF_CONTROL, temp);
> +		I915_WRITE(PCH_DREF_CONTROL, val);
>  		POSTING_READ(PCH_DREF_CONTROL);
>  		udelay(200);
>  	}
> +
> +	BUG_ON(val != final);
>  }
>  
>  /* Sequence to enable CLKOUT_DP for FDI usage and configure PCH FDI I/O. */