Re: [PATCH 01/13] drm/i915: Skip modifying PCH DREF if not changing clock sources

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Wed, 20 Mar 2013 14:17:00 +0200
Imre Deak <imre.deak@intel.com> wrote:

> On Tue, 2013-02-19 at 13:31 -0800, Jesse Barnes wrote:
> > From: Chris Wilson <chris@chris-wilson.co.uk>
> > 
> > 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 3e6dadf..f20555e 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -4758,7 +4758,7 @@ 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;
> > @@ -4801,70 +4801,109 @@ 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;
> > +	}
> 
> This would be clearer in a separate function with a 'check_only' flag,
> then we could do away with the code below.

Yeah, it would shorten things a bit, but since we only have one caller
right now I'll leave that cleanup alone.

-- 
Jesse Barnes, Intel Open Source Technology Center