[Intel-gfx] [PATCH] drm/i915/icl: Add warn about unsupported CDCLK rates

[Imre Deak]

On Thu, Jun 07, 2018 at 08:01:14PM +0300, Ville Syrjälä wrote:
> On Thu, Jun 07, 2018 at 07:13:53PM +0300, Imre Deak wrote:
> > While checking workarounds related to the CDCLK PLL, I noticed that the
> > DMC firmware bits for WA#1183 are missing for SKL. After that I
> > clarified with HW people that it's not needed on SKL, since it doesn't
> > support eDP1.4 which would be the only thing requiring the problematic
> > CDCLK clock rates. So in theory we shouldn't ever choose these
> > frequencies, but add an assert in any case for catching such cases and
> > for documentation.
> > 
> > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_cdclk.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_cdclk.c b/drivers/gpu/drm/i915/intel_cdclk.c
> > index 704ddb4d3ca7..71045c38e233 100644
> > --- a/drivers/gpu/drm/i915/intel_cdclk.c
> > +++ b/drivers/gpu/drm/i915/intel_cdclk.c
> > @@ -2355,6 +2355,16 @@ static int skl_modeset_calc_cdclk(struct drm_atomic_state *state)
> >  	 */
> >  	cdclk = skl_calc_cdclk(min_cdclk, vco);
> >  
> > +	/*
> > +	 * The following CDCLK rates are unsupported on SKL. In theory this
> > +	 * should never happen since only the eDP1.4 2.16 and 4.32Gbps rates
> > +	 * require it, but eDP1.4 is not supported on SKL, see display
> > +	 * WA#1183.
> > +	 */
> > +	if (IS_SKYLAKE(to_i915(state->dev)) &&
> > +	    (cdclk == 308571 || cdclk == 617143))
> > +		DRM_WARN_ONCE("Unsupported CDCLK rate.\n");
> 
> Or just WARN(vco == 8640000) in eg. skl_set_cdclk()?

Ok, can move it there. cdclk==432MHz is not specifically disallowed, so
wouldn't checking cdclk be clearer? Even if it's not used atm.

> > +
> >  	intel_state->cdclk.logical.vco = vco;
> >  	intel_state->cdclk.logical.cdclk = cdclk;
> >  	intel_state->cdclk.logical.voltage_level =
> > -- 
> > 2.13.2
> 
> -- 
> Ville Syrjälä
> Intel