[Intel-gfx] [PATCH v1] drm/i915: Clamp min_cdclk to max_cdclk_freq to unblock 8K

[Lisovskiy, Stanislav]

On Wed, Jul 01, 2020 at 11:44:04AM -0700, Manasi Navare wrote:
> On Wed, Jul 01, 2020 at 02:20:28PM +0200, Maarten Lankhorst wrote:
> > Op 30-06-2020 om 13:26 schreef Stanislav Lisovskiy:
> > > We still need "Bump up CDCLK" workaround otherwise getting
> > > underruns - however currently it blocks 8K as CDCLK = Pixel rate,
> > > in 8K case would require CDCLK to be around 1 Ghz which is not
> > > possible.
> > >
> > > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_cdclk.c | 14 +++++++++++++-
> > >  1 file changed, 13 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> > > index 45f7f33d1144..01a5bc6b08c4 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> > > @@ -2080,9 +2080,21 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
> > >  	 * Explicitly stating here that this seems to be currently
> > >  	 * rather a Hack, than final solution.
> > >  	 */
> > > -	if (IS_TIGERLAKE(dev_priv))
> > > +	if (IS_TIGERLAKE(dev_priv)) {
> > >  		min_cdclk = max(min_cdclk, (int)crtc_state->pixel_rate);
> > >  
> > > +		/*
> > > +		 * Clamp to max_cdclk_freq in order not to break an 8K,
> > > +		 * but still leave W/A at place.
> > > +		 */
> > > +		min_cdclk = min(min_cdclk, (int)dev_priv->max_cdclk_freq);
> > > +
> > > +		/*
> > > +		 * max_cdclk_freq check obviously not needed - just return.
> > > +		 */
> > > +		return min_cdclk;
> > > +	}
> > > +
> > >  	if (min_cdclk > dev_priv->max_cdclk_freq) {
> > >  		drm_dbg_kms(&dev_priv->drm,
> > >  			    "required cdclk (%d kHz) exceeds max (%d kHz)\n",
> > 
> > Wouldn't you just have to halve pixel_rate if bigjoiner flag is set?
> 
> We dont have big joiner patches pulled in yet, this is just for the 2p2p configuration
> 
> Manasi

Also it would make more sense if we wanted this to stay here, however I still want
to believe that some day(R) we figure out proper solution. Otherwise yep, we would
need some logic to check if the pixel rate should be divided and etc..

Stan

> 
> >