From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= <ville.syrjala@linux.intel.com>
Subject: Re: [PATCH v3 3/4] drm/i915: Skip CURBASE write when
 nothing changed
Date: Mon, 15 Sep 2014 16:36:38 +0300
Message-ID: <20140915133638.GG12416@intel.com>
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To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
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On Sat, Sep 13, 2014 at 05:20:10PM +0100, Chris Wilson wrote:
> On Fri, Sep 12, 2014 at 08:53:34PM +0300, ville.syrjala@linux.intel.com w=
rote:
> > From: Ville Syrj=E4l=E4 <ville.syrjala@linux.intel.com>
> > =

> > Only write CURBASE when something about the cursor changed. Also
> > eliminate the unnecessary posting read after writing CURCNTR.
> > =

> > Signed-off-by: Ville Syrj=E4l=E4 <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > =

> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i91=
5/intel_display.c
> > index 82c0ad1..60c1aa4 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -8322,16 +8322,18 @@ static void i9xx_update_cursor(struct drm_crtc =
*crtc, u32 base)
> >  			cntl |=3D CURSOR_PIPE_CSC_ENABLE;
> >  	}
> >  =

> > -	if (intel_crtc->cursor_cntl !=3D cntl) {
> > +	if (intel_crtc->cursor_cntl !=3D cntl)
> >  		I915_WRITE(CURCNTR(pipe), cntl);
> > -		POSTING_READ(CURCNTR(pipe));
> > -		intel_crtc->cursor_cntl =3D cntl;
> > -	}
> > +
> > +	if (intel_crtc->cursor_cntl =3D=3D cntl &&
> > +	    intel_crtc->cursor_base =3D=3D base)
> > +		return;
> =

> I'd vote for doing this first and then
> =

> I915_WRITE(CURCNTR(pipe), cntl);
> =

> unconditionally along with the CURBASE flush.

So you want to write all the cursor registers unconditionally when
anything changes? Would work for CURCNTR, but it would also make
CUR_FBC_CTL stand out like a sore thumb since it can't be written
uncoditionally.

> =

> >  	/* and commit changes on next vblank */
> >  	I915_WRITE(CURBASE(pipe), base);
> >  	POSTING_READ(CURBASE(pipe));
> >  =

> > +	intel_crtc->cursor_cntl =3D cntl;
> >  	intel_crtc->cursor_base =3D base;
> >  }
> =

> -- =

> Chris Wilson, Intel Open Source Technology Centre

-- =

Ville Syrj=E4l=E4
Intel OTC