[Intel-gfx] [PATCH 2/2] drm/i915: Parse max HDMI TMDS clock from VBT

[Ville Syrjälä]

On Thu, Oct 26, 2017 at 04:44:39PM +0100, Chris Wilson wrote:
> Quoting Ville Syrjala (2017-10-26 16:14:05)
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > Starting from version 204 VBT can specify the max TMDS clock we are
> > allowed to use with HDMI ports. Parse that information and take it
> > into account when filtering modes and computing a crtc state.
> >  
> > +       if (bdb_version >= 204) {
> > +               int max_tmds_clock;
> > +
> > +               switch (child->hdmi_max_data_rate) {
> > +               case 1:
> > +                       max_tmds_clock = 297000;
> > +                       break;
> > +               case 2:
> > +                       max_tmds_clock = 165000;
> > +                       break;
> > +               default:
> > +                       max_tmds_clock = 0;
> 
> Is zero a valid value, as this will prevent us from using the output
> at all?

Zero means "unlimited" or "use the platform default maximum". The code
using this will check to make sure it's non-zero before doing the min().

We use similar logic in hdmi_port_clock_limit() to handle the sink and
dongle limits.

-- 
Ville Syrjälä
Intel OTC