[Intel-gfx] [PATCH] Lower threshold for pixel doubling.

[Daniel Vetter]

On Tue, May 28, 2013 at 10:39:07AM -0700, Stuart Abercrombie wrote:
> Any comments?
> 
> Without this, plugging one of the older Chromebook models into a Dell U3011
> monitor produces a garbled display at the default 2048x1280 resolution.
> 
> The original threshold was apparently fairly arbitrary:
> 
> http://cgit.freedesktop.org/~anholt/xf86-video-intel/commit/?id=8fcf9a81179ee8577ddab5e904c58fbfd14cf59c

Do you see any pipe underruns without this patch? There are some not-yet
implemented tricks we should be pulling around re-splitting DSP_ARB fifo
entries, which tend to totally kill high-res modes.
-Daniel

> .
> 
> Stuart
> 
> 
> On Mon, May 20, 2013 at 11:15 AM, Stuart Abercrombie <
> sabercrombie at chromium.org> wrote:
> 
> > 90% of core speed (=180MHz dot clock) is too high for 2048x1280 to get
> > pixel doubling on Pineview, which it needs to avoid underruns, so
> > lower this to 85%.
> >
> > Signed-off-by: Stuart Abercrombie <sabercrombie at chromium.org>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > b/drivers/gpu/drm/i915/intel_display.c
> > index efe8299..9c924e9 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -4564,14 +4564,14 @@ static void i9xx_set_pipeconf(struct intel_crtc
> > *intel_crtc)
> >         pipeconf = I915_READ(PIPECONF(intel_crtc->pipe));
> >
> >         if (intel_crtc->pipe == 0 && INTEL_INFO(dev)->gen < 4) {
> > -               /* Enable pixel doubling when the dot clock is > 90% of
> > the (display)
> > +               /* Enable pixel doubling when the dot clock is > 85% of
> > the (display)
> >                  * core speed.
> >                  *
> >                  * XXX: No double-wide on 915GM pipe B. Is that the only
> > reason for the
> >                  * pipe == 0 check?
> >                  */
> >                 if (intel_crtc->config.requested_mode.clock >
> > -                   dev_priv->display.get_display_clock_speed(dev) * 9 /
> > 10)
> > +                   dev_priv->display.get_display_clock_speed(dev) * 17 /
> > 20)
> >                         pipeconf |= PIPECONF_DOUBLE_WIDE;
> >                 else
> >                         pipeconf &= ~PIPECONF_DOUBLE_WIDE;
> > --
> > 1.8.2.1
> >
> >

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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch