drm/i915/dp: Be smarter about connection sense for branch devices

If there's no downstream device, DPCD success is good enough.  If
there's a hotplug-capable downstream device, count the number of
connected sinks in DP_SINK_STATUS and return success if it's non-zero.
Otherwise, probe DDC and report appropriately.

v2: Check DP_SINK_STATUS instead of something unrelated to sink status.

Tested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 42bdca47c5d6d90437a7da84528a07b614e72359..4f2a38181491866c7f5480da98529abc31219e70 100644 (file)
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2083,11 +2083,44 @@ 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) {
+               uint8_t sink_count;
+               if (!intel_dp_aux_native_read_retry(intel_dp, DP_SINK_COUNT,
+                                                   &sink_count, 1))
+                       return connector_status_unknown;
+               sink_count &= DP_SINK_COUNT_MASK;
+               return sink_count ? connector_status_connected
+                                 : connector_status_disconnected;
+       }
+
+       /* 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;
 }