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

[Stuart Abercrombie]

Without this change I saw PIPE_FIFO_UNDERRUN_STATUS set in PIPEASTAT, which
I took to indicate an underrun problem.

Here's what I found with other modes on this monitor:

1920x1200 works with pixel doubling enabled. Pixel clock 193.2 MHz.
2048x1152 works with pixel doubling enabled. Pixel clock 198.0 MHz.
1600x1200 works with pixel doubling disabled. Pixel clock 162.0 MHz.
2048x1280 fails with pixel doubling disabled. PIxel clock 174.2 MHz..

Based on this, it seems the threshold needs to be be between 162.0MHz and
174.2MHz, whereas currently it's at 180MHz.  The change puts it at 170MHz.

Stuart


On Wed, May 29, 2013 at 8:22 AM, Daniel Vetter <daniel at ffwll.ch> wrote:

> 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
> > >
> > >
>
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>
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