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

[Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>]

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 ?

-- 
regards,
Sivakumar

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