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

[ville.syrjala at linux.intel.com]

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;
 		}
 	}
 
-- 
2.3.6