Re: [PATCH] drm/i915/glk: Don't allow 12 bpc when htotal is too big

[Ander Conselvan De Oliveira <conselvan2@gmail.com>]

On Mon, 2017-04-24 at 16:49 +0530, Sharma, Shashank wrote:
> Regards
> 
> Shashank
> 
> 
> On 4/24/2017 4:17 PM, Ander Conselvan de Oliveira wrote:
> > Display workaround #1139 for Geminilake instructs us to restrict HDMI
> > to 8 bpc when htotal is greater than 5460. Otherwise, the pipe is unable
> > to generate a proper signal and is left in a state where corruption is
> > seen with other modes.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100440
> > Cc: Shashank Sharma <shashank.sharma@intel.com>
> > Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
> > ---
> >   drivers/gpu/drm/i915/intel_hdmi.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
> > index 6efc3cb..52f0b2d 100644
> > --- a/drivers/gpu/drm/i915/intel_hdmi.c
> > +++ b/drivers/gpu/drm/i915/intel_hdmi.c
> > @@ -1327,6 +1327,11 @@ static bool hdmi_12bpc_possible(struct intel_crtc_state *crtc_state)
> >   			return false;
> >   	}
> >   
> > +	/* Display Wa #1139 */
> > +	if (IS_GLK_REVID(dev_priv, 0, GLK_REVID_A1) &&
> > +	    crtc_state->base.adjusted_mode.htotal > 5460)
> 
> Small inputs:
> - We might wanna extend this for CNL too, as the WAR is valid for it 
> too. I am not sure it should be this same patch or not.

None of the CNL patches landed yet, so I think we should include this in the
patch/series that enables hdmi 2.0 clocks for it.

> - We need to modify this check not to affect the YCBCR 420 modes, as 
> there won't be any change between the timings of a YCBCR mode and a
>    normal mode (apart from a flag), but htotal should be valid in YCBCR 
> 420 case. But I can handle this part while sending second patch set of
>    YCBCR 420 handling.

Thanks.

> - Also, should we reject 12BPC totally, or just clamp htotal to max 
> possible (5460) and go ahead? Ville ?

Since this is only up to GLK A1, I don't think it is worth the trouble.

Ander

> 
> In any case, please feel free to use:
> Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
> > +		return false;
> > +
> >   	return true;
> >   }
> >   
> 
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