[Intel-gfx] [PATCH] drm/i915: More cautious with pch fifo underruns

[Paulo Zanoni]

2014-11-24 14:02 GMT-02:00 Daniel Vetter <daniel.vetter at ffwll.ch>:
> Apparently PCH fifo underruns are tricky, we have plenty reports that
> we see the occasional underrun (especially at boot-up).
>
> So for a change let's see what happens when we don't re-enable pch
> fifo underrun reporting when the pipe is disabled.

Does that mean you don't really know if this patch is going to fix something?

I see what this patch does, but I don't really see what is its
benefit, besides "we'll get less bug reports". Is there any reason why
the underruns are expected to happen at this time?

Please explain a little more.

> This means that the
> kernel can't catch pch fifo underruns when they happen (except when
> all pipes are on on the pch). But we'll still catch underruns when
> disabling the pipe again.

Are you sure the sentences above are correct?


> So not a terrible reduction in test
> coverage.

Yeah, I agree, but please provide a nice reason for it :)

>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=85898
> References: https://bugs.freedesktop.org/show_bug.cgi?id=86233
> References: https://bugs.freedesktop.org/show_bug.cgi?id=86478
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 320bf4c78c8c..a4106049e158 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -4501,7 +4501,6 @@ static void ironlake_crtc_disable(struct drm_crtc *crtc)
>                 ironlake_fdi_disable(crtc);
>
>                 ironlake_disable_pch_transcoder(dev_priv, pipe);
> -               intel_set_pch_fifo_underrun_reporting(dev_priv, pipe, true);
>
>                 if (HAS_PCH_CPT(dev)) {
>                         /* disable TRANS_DP_CTL */
> @@ -4572,8 +4571,6 @@ static void haswell_crtc_disable(struct drm_crtc *crtc)
>
>         if (intel_crtc->config.has_pch_encoder) {
>                 lpt_disable_pch_transcoder(dev_priv);
> -               intel_set_pch_fifo_underrun_reporting(dev_priv, TRANSCODER_A,
> -                                                     true);
>                 intel_ddi_fdi_disable(crtc);
>         }
>
> --
> 2.1.1
>
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-- 
Paulo Zanoni