Re: [PATCH] drm/i915/psr: Preserve SRD_CTL bit 29 on PSR init

[Jim Bride <jim.bride@linux.intel.com>]

On Tue, Aug 08, 2017 at 07:42:50PM +0000, Vivi, Rodrigo wrote:
> On Tue, 2017-08-08 at 08:51 -0700, Jim Bride wrote:
> > Bit 29 of SRD_CTL needs to have its value preserved,
> 
> probably good to kind of quote spec somehow:
> "This field is used for hardware communication.  Software must not
> change this field."

Added "according to the B-Spec" after the word preserved.
> 
> >  so right before we
> > write out the register we go ahead and read the register and preserve
> > the value of that bit before we write out the configured register value.
> > 
> > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Signed-off-by: Jim Bride <jim.bride@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_reg.h  | 1 +
> >  drivers/gpu/drm/i915/intel_psr.c | 1 +
> >  2 files changed, 2 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > index b2546ad..ea8e421 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -3872,6 +3872,7 @@ enum {
> >  #define EDP_PSR_CTL				_MMIO(dev_priv->psr_mmio_base + 0)
> >  #define   EDP_PSR_ENABLE			(1<<31)
> >  #define   BDW_PSR_SINGLE_FRAME			(1<<30)
> > +#define   EDP_PSR_RESTORE_PSR_ACTIVE_CTX        (1<<29) /* SW can't modify */
> 
> - please use real tabs instead of spaces.

Not sure what happened there, but fixed.

> 
> - a MASK on the name is better since we are not using this define to set
> the bit, but to mask instead.

Changed as per suggesation.

> >  #define   EDP_PSR_LINK_STANDBY			(1<<27)
> >  #define   EDP_PSR_MIN_LINK_ENTRY_TIME_MASK	(3<<25)
> >  #define   EDP_PSR_MIN_LINK_ENTRY_TIME_8_LINES	(0<<25)
> > diff --git a/drivers/gpu/drm/i915/intel_psr.c b/drivers/gpu/drm/i915/intel_psr.c
> > index 559f1ab..0d08efa 100644
> > --- a/drivers/gpu/drm/i915/intel_psr.c
> > +++ b/drivers/gpu/drm/i915/intel_psr.c
> > @@ -315,6 +315,7 @@ static void intel_enable_source_psr1(struct intel_dp *intel_dp)
> >  	else
> >  		val |= EDP_PSR_TP1_TP2_SEL;
> >  
> 
> I wondered if we should add an extra comment here, but I believe it is
> not necessary if we have the "_MASK" on the bit name.

I think it would be redundant with the comment in i915_reg.h, which I
believe to be a better place for the note.  In any event, a new version
of the patch is coming with the above changes  once I smoke-test
everything again.

Jim

> > +	val |= I915_READ(EDP_PSR_CTL) & EDP_PSR_RESTORE_PSR_ACTIVE_CTX;
> >  	I915_WRITE(EDP_PSR_CTL, val);
> >  }
> >  
> 
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