[Intel-gfx] [PATCH 4/4] drm/i915/dp: Be smarter about connection sense for branch devices

[Adam Jackson]

Signed-off-by: Adam Jackson <ajax at redhat.com>
---
 drivers/gpu/drm/i915/intel_dp.c |   28 +++++++++++++++++++++++++++-
 1 files changed, 27 insertions(+), 1 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 92939bd..9809c53 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2088,11 +2088,37 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 	}
 }
 
+/* XXX this is probably wrong for multiple downstream ports */
 static enum drm_connector_status
 intel_dp_detect_dpcd(struct intel_dp *intel_dp)
 {
-	if (intel_dp_get_dpcd(intel_dp))
+	uint8_t *dpcd = intel_dp->dpcd;
+	bool hpd;
+	uint8_t type;
+
+	if (!intel_dp_get_dpcd(intel_dp))
+		return connector_status_disconnected;
+	
+	/* if there's no downstream port, we're done */
+	if (!(dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT))
 		return connector_status_connected;
+
+	/* If we're HPD-aware, SINK_COUNT changes dynamically */
+	hpd = !!(intel_dp->downstream_ports[0] & DP_DS_PORT_HPD);
+	if (hpd && (intel_dp->link_configuration[0] & DP_SINK_COUNT_MASK))
+		return connector_status_connected;
+
+	/* If no HPD, poke DDC gently */
+	if (drm_probe_ddc(&intel_dp->adapter))
+		return connector_status_connected;
+
+	/* Well we tried, say unknown for unreliable port types */
+	type = intel_dp->downstream_ports[0] & DP_DS_PORT_TYPE_MASK;
+	if (type == DP_DS_PORT_TYPE_VGA || type == DP_DS_PORT_TYPE_NON_EDID)
+		return connector_status_unknown;
+
+	/* Anything else is out of spec, warn and ignore */
+	DRM_DEBUG_KMS("Broken DP branch device, ignoring\n");
 	return connector_status_disconnected;
 }
 
-- 
1.7.7.6