[PATCH v4 09/11] drm/i915: Check pixel rate for DP to VGA dongle

[Kahola, Mika]

> -----Original Message-----
> From: Ville Syrjälä [mailto:ville.syrjala at linux.intel.com]
> Sent: Thursday, June 9, 2016 11:14 AM
> To: Kahola, Mika <mika.kahola at intel.com>
> Cc: dri-devel at lists.freedesktop.org; intel-gfx at lists.freedesktop.org;
> jim.bride at linux.intel.com; daniel.vetter at ffwll.ch
> Subject: Re: [PATCH v4 09/11] drm/i915: Check pixel rate for DP to VGA
> dongle
> 
> On Mon, Jun 06, 2016 at 04:29:11PM +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)
> >
> > Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > b/drivers/gpu/drm/i915/intel_dp.c index 096acbf0..1b94347 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -200,6 +200,23 @@ intel_dp_mode_valid(struct drm_connector
> *connector,
> >  	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;
> > +	bool is_branch_device;
> > +	int max_dp_clk;
> > +	int type;
> > +	uint8_t port_cap[4];
> > +
> > +	is_branch_device = intel_dp-
> >dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> > +		DP_DWN_STRM_PORT_PRESENT;
> > +
> > +	if (is_branch_device) {
> > +		drm_dp_downstream_port_cap(&intel_dp->aux, intel_dp-
> >dpcd,
> > +port_cap);
> 
> I'm pretty sure we already read out the downstream port caps in fact.
> Hmm, yeah ->downstream_ports. So no need for this, and I suppose no
> need for your helper for the readout either. Just always readoing out the full
> 16 bytes should be fine.

Right, I missed that one. We do read port caps with ->downstream_ports. I'll skip the helper routines regarding reading out port cap info.

> 
> > +		type = drm_dp_downstream_type(intel_dp->dpcd,
> port_cap);
> > +		max_dp_clk = drm_dp_downstream_max_clock(intel_dp-
> >dpcd, port_cap);
> > +
> > +		if ((type == DP_DS_PORT_TYPE_VGA) && (max_dp_clk > 0))
> {
> 
> Type check can be skipped if drm_dp_downstream_max_clock() just returns
> 0 for the "don't know" case.
> 
> > +			max_dotclk = min(max_dotclk, max_dp_clk);
> > +		}
> > +	}
> >
> >  	if (is_edp(intel_dp) && fixed_mode) {
> >  		if (mode->hdisplay > fixed_mode->hdisplay)
> > --
> > 1.9.1
> 
> --
> Ville Syrjälä
> Intel OTC