Re: [Intel-gfx] [PATCH] Revert "drm/i915: Remove unneeded hack now for CDCLK"

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 08 Jun 2020, "Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com> wrote:
> On Mon, Jun 08, 2020 at 11:21:14AM +0300, Jani Nikula wrote:
>> On Mon, 08 Jun 2020, Stanislav Lisovskiy <stanislav.lisovskiy@intel.com> wrote:
>> > This reverts commit 82ea174dc5425d4e85e25d0c4ba961a2e494392a.
>> >
>> 
>> Please explain why. What's going on, why we need the revert.
>> 
>> It's fine to reply here, the commit message can be amended by whoever
>> applies the patch.
>
> Yes, 
>
> Unfortunately according to our recent findings there is still some
> unidentified factor, requiring CDCLK to be set higher - otherwise we 
> still get underruns on some multipipe configurations, despite CDCLK being set
> according to BSpec formula. So getting again back into debug mode to
> indentify the cause, meanwhile setting CDCLK=Pixel rate back in order
> to remove regression in 10% of the cases due to FIFO underruns.

Thanks, pushed.

BR,
Jani.


>
> Stan 
>
>> 
>> BR,
>> Jani.
>> 
>> 
>> > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
>> > Fixes: cd1915460861 ("drm/i915: Adjust CDCLK accordingly to our DBuf bw needs")
>> > ---
>> >  drivers/gpu/drm/i915/display/intel_cdclk.c | 12 ++++++++++++
>> >  1 file changed, 12 insertions(+)
>> >
>> > diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
>> > index 08468b121d02..45f7f33d1144 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
>> > +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
>> > @@ -2071,6 +2071,18 @@ 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 = max(min_cdclk, (int)crtc_state->pixel_rate);
>> > +
>> >  	if (min_cdclk > dev_priv->max_cdclk_freq) {
>> >  		drm_dbg_kms(&dev_priv->drm,
>> >  			    "required cdclk (%d kHz) exceeds max (%d kHz)\n",
>> 
>> -- 
>> Jani Nikula, Intel Open Source Graphics Center

-- 
Jani Nikula, Intel Open Source Graphics Center
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