Re: [PATCH] drm/i915: Improve DP downstream HPD handling

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Jul 07, 2015 at 03:26:36PM +0530, Sivakumar Thulasimani wrote:
> 
> 
> On 7/6/2015 5:42 PM, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > DP dongles may signal downstream HPD via short HPD pulses. If we know
> > the device has a HPD capable downstream port, make sure we kick off the
> > full hotplug processing even for short HPDs.
> >
> > Additonally setting the sink to DPMS off kills the downstream HPD (at
> > least on my DP->VGA dongle), so skip the DPMS off for such dongles
> > when we turn off the port.
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/intel_dp.c | 18 +++++++++++++++++-
> >   1 file changed, 17 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index e88cec2..f424833 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -2324,6 +2324,13 @@ static void intel_dp_get_config(struct intel_encoder *encoder,
> >   	}
> >   }
> >   
> > +static bool intel_dp_has_downstream_hpd(struct intel_dp *intel_dp)
> > +{
> > +	return intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT &&
> > +		intel_dp->dpcd[DP_DPCD_REV] >= 0x11 &&
> > +		intel_dp->downstream_ports[0] & DP_DS_PORT_HPD;
> > +}
> > +
> >   static void intel_disable_dp(struct intel_encoder *encoder)
> >   {
> >   	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
> > @@ -2340,7 +2347,9 @@ static void intel_disable_dp(struct intel_encoder *encoder)
> >   	 * ensure that we have vdd while we switch off the panel. */
> >   	intel_edp_panel_vdd_on(intel_dp);
> >   	intel_edp_backlight_off(intel_dp);
> > -	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
> > +	/* Skip power down to keep downstream HPD working */
> > +	if (!intel_dp_has_downstream_hpd(intel_dp))
> > +		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_OFF);
> >   	intel_edp_panel_off(intel_dp);
> >   
> >   	/* disable the port before the pipe on g4x */
> > @@ -4944,6 +4953,13 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
> >   			drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
> >   			intel_dp_check_link_status(intel_dp);
> >   			drm_modeset_unlock(&dev->mode_config.connection_mutex);
> > +
> > +			/*
> > +			 * Downstream HPD will generate a short HPD,
> > +			 * so we want full hotplug processing here.
> > +			 */
> > +			if (intel_dp_has_downstream_hpd(intel_dp))
> > +				goto put_power;
> >   		}
> >   	}
> >   
> I am looking into compliance changes for DP and this seems a relevant 
> change for compliance as well. but as per Link CTS 1.2 section 4.2.2.8, 
> we are supposed to read the sink_count and do full detection if 
> sink_count is >1.  So instead of checking for DP_DS_PORT_HPD can we just 
> check SINK_COUNT and do full detect ?

->detect() will be called from the hotplug work and that will
check SINK_COUNT.

-- 
Ville Syrjälä
Intel OTC
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