[Intel-gfx] [PATCH 5/6] drm/i915: read sink_count dpcd always

[Shubhangi Shrivastava]

This patch reads sink_count dpcd always and removes its
read operation based on values in downstream port dpcd.

SINK_COUNT dpcd is not dependent on DOWNSTREAM_PORT_PRESENT dpcd.
SINK_COUNT denotes if a display is attached, while
DOWNSTREAM_PORT_PRESET indicates how many ports are available
in the dongle where display can be attached. so it is possible
for sink count to change irrespective of value in downstream
port dpcd.

Here is a table of possible values and scenarios

sink_count      downstream_port
                present
0               0               no display is attached
0               1               dongle is connected without display
1               0               display connected directly
1               1               display connected through dongle

Tested-by: Nathan D Ciobanu <nathan.d.ciobanu at intel.com>
Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani at intel.com>
Signed-off-by: Shubhangi Shrivastava <shubhangi.shrivastava at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index c2e8516..0d58bfd 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3865,6 +3865,13 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
 	if (intel_dp->dpcd[DP_DPCD_REV] == 0)
 		return false; /* DPCD not present */
 
+	if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_SINK_COUNT,
+				    &intel_dp->sink_count, 1) < 0)
+		return false;
+
+	if (!DP_GET_SINK_COUNT(intel_dp->sink_count))
+		return false;
+
 	/* Check if the panel supports PSR */
 	memset(intel_dp->psr_dpcd, 0, sizeof(intel_dp->psr_dpcd));
 	if (is_edp(intel_dp)) {
@@ -4386,10 +4393,6 @@ intel_dp_detect_dpcd(struct intel_dp *intel_dp)
 	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11 &&
 	    intel_dp->downstream_ports[0] & DP_DS_PORT_HPD) {
 
-		if (intel_dp_dpcd_read_wake(&intel_dp->aux, DP_SINK_COUNT,
-					    &intel_dp->sink_count, 1) < 0)
-			return connector_status_unknown;
-
 		return DP_GET_SINK_COUNT(intel_dp->sink_count) ?
 		connector_status_connected : connector_status_disconnected;
 	}
-- 
2.6.1