[PATCH v7 3/5] drm/i915: Check pixel rate for DP to VGA dongle

[Mika Kahola]

On Thu, 2016-08-11 at 10:18 +0300, Ville Syrjälä wrote:
> On Mon, Aug 08, 2016 at 04:00:28PM +0300, Mika Kahola wrote:
> > Filter out a mode that exceeds the max pixel rate setting
> > for DP to VGA dongle. This is defined in DPCD register 0x81
> > if detailed cap info i.e. info field is 4 bytes long and
> > it is available for DP downstream port.
> > 
> > The register defines the pixel rate divided by 8 in MP/s.
> > 
> > v2: DPCD read outs and computation moved to drm (Ville, Daniel)
> > v3: Sink pixel rate computation moved to drm_dp_max_sink_dotclock()
> >     function (Daniel)
> > v4: Use of drm_dp_helper.c routines to compute max pixel clock (Ville)
> > v5: Use of intel_dp->downstream_ports to read out port capabilities.
> >     Code restructuring (Ville)
> > v6: Move DP branch device check to drm_dp_helper.c (Daniel)
> > 
> > Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 25 ++++++++++++++++++++++++-
> >  1 file changed, 24 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 21b04c3..e990c8b 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -190,6 +190,26 @@ intel_dp_max_data_rate(int max_link_clock, int max_lanes)
> >  	return (max_link_clock * max_lanes * 8) / 10;
> >  }
> >  
> > +static int
> > +intel_dp_downstream_max_dotclock(struct intel_dp *intel_dp, int dotclk)
> > +{
> 
> I would just
> 
> {
> 	int max_dotclk = dev_priv->max_dotclk_freq;
> 
> 	ds_max_dotclk = ...;
> 	if (ds_dotclk != 0)
> 		max_dotclk = min(max_dotclk, ds_max_dotclk);
> 
> 	return max_dotclk;
> }
> 
> > +	int ds_dotclk;
> > +	int type;
> > +
> > +	ds_dotclk = drm_dp_downstream_max_clock(intel_dp->dpcd,
> > +						intel_dp->downstream_ports);
> > +
> > +	if (ds_dotclk == 0)
> > +		return dotclk;
> > +
> > +	type = intel_dp->downstream_ports[0] & DP_DS_PORT_TYPE_MASK;
> > +	
> > +	if (type != DP_DS_PORT_TYPE_VGA)
> > +		return dotclk;
> 
> Why isn't drm_dp_downstream_max_clock() handling all of it already?
> Why are we even checking for !=VGA?
The routine drm_dp_downstream_max_clock returns the clock rate which can
be dotclock (VGA only) or TMDS clock (for DVI, HDMI, DP++). Here, we
need to have a check for this as we are only interested to update VGA
dotclock value.

Cheers,
Mika
> 
> > +
> > +	return min(dotclk, ds_dotclk);
> > +}
> > +
> >  static enum drm_mode_status
> >  intel_dp_mode_valid(struct drm_connector *connector,
> >  		    struct drm_display_mode *mode)
> > @@ -199,7 +219,10 @@ intel_dp_mode_valid(struct drm_connector *connector,
> >  	struct drm_display_mode *fixed_mode = intel_connector->panel.fixed_mode;
> >  	int target_clock = mode->clock;
> >  	int max_rate, mode_rate, max_lanes, max_link_clock;
> > -	int max_dotclk = to_i915(connector->dev)->max_dotclk_freq;
> > +	int max_dotclk;
> > +
> > +	max_dotclk = intel_dp_downstream_max_dotclock(intel_dp,
> > +						      to_i915(connector->dev)->max_dotclk_freq);
> >  
> >  	if (is_edp(intel_dp) && fixed_mode) {
> >  		if (mode->hdisplay > fixed_mode->hdisplay)
> > -- 
> > 1.9.1
>