On Thu, 09 Jan 2020, Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx> wrote: > There seems to be some undocumented bandwidth > bottleneck/dependency which scales with CDCLK, > causing FIFO underruns when CDCLK is too low, > even when it's correct from BSpec point of view. > > Currently for TGL platforms we calculate > min_cdclk initially based on pixel_rate divided > by 2, accounting for also plane requirements, > however in some cases the lowest possible CDCLK > doesn't work and causing the underruns. > > Explicitly stating here that this seems to be currently > rather a Hack, than final solution. > > v2: Use clamp operation instead of min(Matt Roper) > > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx> > Bugzilla: https://gitlab.freedesktop.org/drm/intel/issues/402 > --- > drivers/gpu/drm/i915/display/intel_cdclk.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c > index 7d1ab1e5b7c3..23ef30175090 100644 > --- a/drivers/gpu/drm/i915/display/intel_cdclk.c > +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c > @@ -2004,6 +2004,20 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state) > /* Account for additional needs from the planes */ > min_cdclk = max(intel_planes_min_cdclk(crtc_state), min_cdclk); > > + /* > + * HACK. Currently for TGL platforms we calculate > + * min_cdclk initially based on pixel_rate divided > + * by 2, accounting for also plane requirements, > + * however in some cases the lowest possible CDCLK > + * doesn't work and causing the underruns. > + * Explicitly stating here that this seems to be currently > + * rather a Hack, than final solution. > + */ > + if (IS_TIGERLAKE(dev_priv)) > + min_cdclk = clamp(min_cdclk, > + (int)crtc_state->pixel_rate, > + (int)dev_priv->max_cdclk_freq); I don't think you can do that even as a hack. By clamping the required minimum to the max cdclk, you lose the check below. Can't do that. BR, Jani. > + > if (min_cdclk > dev_priv->max_cdclk_freq) { > DRM_DEBUG_KMS("required cdclk (%d kHz) exceeds max (%d kHz)\n", > min_cdclk, dev_priv->max_cdclk_freq); -- Jani Nikula, Intel Open Source Graphics Center _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
