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>

1 files changed, 34 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 42bdca47c5d6..4f2a38181491 100644
--- 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;
 }