[Intel-gfx] [PATCH] drm/i915: Improve DP downstream HPD handling

[Ville Syrjälä]

On Tue, Jul 07, 2015 at 04:45:11PM +0530, Sivakumar Thulasimani wrote:
> 
> 
> On 7/7/2015 4:40 PM, Ville Syrjälä wrote:
> > On Tue, Jul 07, 2015 at 03:26:36PM +0530, Sivakumar Thulasimani wrote:
> >>
> >> On 7/6/2015 5:42 PM, ville.syrjala at linux.intel.com wrote:
> >>> From: Ville Syrjälä <ville.syrjala at 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 at 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.
> >
> No, the Compliance Sink tool, will not set the DP_DS_PORT_HPD resulting 
> in detect not getting executed for
> the short pulse generated. The spec requires the sink to set only the 
> sink count so it is not a must for
> the sink to update the DP_DOWNSTREAM_PORT_0. so only a check for 
> SINK_COUNT will pass the
> compliance test.

That seems stupid. If the downstream port isn't HPD capable then we have
no reason to check SINK_COUNT after a short HPD as the short HPD
coudln't have been caused by a downstram HPD. Obviuously we still
check SINK_COUNT after a long HPD to figure out if anything is connected
when the branch device itself gets connected to the source.

-- 
Ville Syrjälä
Intel OTC