[PATCH 3/4] drm/i915/dp: Fetch downstream port info if needed during DPCD fetch

[Adam Jackson]

v2: Fix parenthesis mismatch, spotted by Jani Nikula

Tested-by: Takashi Iwai <tiwai at suse.de>
Signed-off-by: Adam Jackson <ajax at redhat.com>
---
 drivers/gpu/drm/i915/intel_dp.c |   25 ++++++++++++++++++++-----
 1 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index ace757a..098119e 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -39,6 +39,7 @@
 #include "drm_dp_helper.h"
 
 #define DP_RECEIVER_CAP_SIZE	0xf
+#define DP_MAX_DOWNSTREAM_PORTS 0xf
 #define DP_LINK_STATUS_SIZE	6
 #define DP_LINK_CHECK_TIMEOUT	(10 * 1000)
 
@@ -56,6 +57,7 @@ struct intel_dp {
 	uint8_t link_bw;
 	uint8_t lane_count;
 	uint8_t dpcd[DP_RECEIVER_CAP_SIZE];
+	uint8_t downstream_ports[DP_MAX_DOWNSTREAM_PORTS];
 	struct i2c_adapter adapter;
 	struct i2c_algo_dp_aux_data algo;
 	bool is_pch_edp;
@@ -1968,12 +1970,25 @@ static bool
 intel_dp_get_dpcd(struct intel_dp *intel_dp)
 {
 	if (intel_dp_aux_native_read_retry(intel_dp, 0x000, intel_dp->dpcd,
-					   sizeof(intel_dp->dpcd)) &&
-	    (intel_dp->dpcd[DP_DPCD_REV] != 0)) {
-		return true;
-	}
+					   sizeof(intel_dp->dpcd)) == 0)
+		return false; /* aux transfer failed */
 
-	return false;
+	if (intel_dp->dpcd[DP_DPCD_REV] == 0)
+		return false; /* DPCD not present */
+
+	if (!(intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
+	      DP_DWN_STRM_PORT_PRESENT))
+		return true; /* native DP sink */
+
+	if (intel_dp->dpcd[DP_DPCD_REV] == 0x10)
+		return true; /* no per-port downstream info */
+
+	if (intel_dp_aux_native_read_retry(intel_dp, DP_DOWNSTREAM_PORT_0,
+					   intel_dp->downstream_ports,
+					   DP_MAX_DOWNSTREAM_PORTS) == 0)
+		return false; /* downstream port status fetch failed */
+
+	return true;
 }
 
 static void
-- 
1.7.7.6