drm/i915/dp: retry link status read 3 times on failure

Especially after a hotplug or power status change, the sink may not
reply immediately to a link status query.  So retry 3 times per the spec
to really make sure nothing is there.

See section 9.1 of the 1.1a DisplayPort spec.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 13 insertions, 7 deletions

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 391b55f1cc74..86912bd737ad 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1019,14 +1019,20 @@ intel_dp_dpms(struct drm_encoder *encoder, int mode)
 static bool
 intel_dp_get_link_status(struct intel_dp *intel_dp)
 {
-        int ret;
+        int ret, i;
+
+        /* Must try AUX reads for this at least 3 times */
+        for (i = 0; i < 3; i++) {
+                ret = intel_dp_aux_native_read(intel_dp,
+                                               DP_LANE0_1_STATUS,
+                                               intel_dp->link_status,
+                                               DP_LINK_STATUS_SIZE);
+                if (ret == DP_LINK_STATUS_SIZE)
+                        return true;
+                msleep(1);
+        }
 
-        ret = intel_dp_aux_native_read(intel_dp,
-                                       DP_LANE0_1_STATUS,
-                                       intel_dp->link_status, DP_LINK_STATUS_SIZE);
-        if (ret != DP_LINK_STATUS_SIZE)
-                return false;
-        return true;
+        return false;
 }
 
 static uint8_t