The short pulse handler checks if channel equalization is okay and
goes onto retrain a link if there are active MST links. This retraining
path is not meant for new MST connections, but due to a bug elsewhere, if
active_mst_links is < 0 the boolean check for active_mst_links passes and
we proceed to retrain a new link. This results in a sequence of failed link
training attempts, most likely due to the hardware not setup for link
training at that point i.e., missing the DDI pre_enable sequence.
[ 80.301272] [drm:intel_dp_check_mst_status] channel EQ not ok, retraining
[ 80.301312] [drm:intel_ddi_prepare_link_retrain] *ERROR* Timeout waiting for DDI BUF C idle bit
The above error gives us a hint something went wrong before link
training started.
Check for a positive value of active_mst_links and throw in a warning for
invalid active_mst_links as debug aid.
Cc: Nathan Ciobanu <nathan.d.ciobanu@xxxxxxxxxxxxxxx>
Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_dp.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index b45b08420c1f..2d61ff01cf51 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4213,12 +4213,14 @@ intel_dp_check_mst_status(struct intel_dp *intel_dp)
int ret = 0;
int retry;
bool handled;
+
+ WARN_ON_ONCE(intel_dp->active_mst_links < 0);
bret = intel_dp_get_sink_irq_esi(intel_dp, esi);
go_again:
if (bret == true) {
/* check link status - esi[10] = 0x200c */
- if (intel_dp->active_mst_links &&
+ if (intel_dp->active_mst_links > 0 &&
!drm_dp_channel_eq_ok(&esi[10], intel_dp->lane_count)) {
DRM_DEBUG_KMS("channel EQ not ok, retraining\n");
intel_dp_start_link_train(intel_dp);
--
2.17.1
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