[PATCH] drm/i915/dp: Give up link training clock recovery after 10 failed attempts

[Nathan Ciobanu]

Limit the link training clock recovery loop to 10 failed attempts at
LANEx_CR_DONE per DP 1.4 spec. Some USB-C MST hubs cause us to get
stuck in this loop on hot-plugging indefinitely as
drm_dp_clock_recovery_ok() never returns true and none of the
other conditions occur.

Signed-off-by: Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_dp_link_training.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
index 4da6e33c7fa1..66c1a70343ba 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -129,7 +129,7 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
 intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
 {
 	uint8_t voltage;
-	int voltage_tries, max_vswing_tries;
+	int voltage_tries, max_vswing_tries, cr_tries;
 	uint8_t link_config[2];
 	uint8_t link_bw, rate_select;
 
@@ -172,6 +172,7 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
 
 	voltage_tries = 1;
 	max_vswing_tries = 0;
+	cr_tries = 0;
 	for (;;) {
 		uint8_t link_status[DP_LINK_STATUS_SIZE];
 
@@ -215,6 +216,11 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
 		if (intel_dp_link_max_vswing_reached(intel_dp))
 			++max_vswing_tries;
 
+		if (cr_tries == 9) {
+			DRM_ERROR("Failed clock recovery 10 times, giving up!\n");
+			return false;
+		}
+		++cr_tries;
 	}
 }
 
-- 
1.9.1