drm/amd/display: lower lane count first when CR done partially fails in EQ

[why]
According to DP specs, in EQ DONE phase of link training, we
should lower lane count when at least one CR DONE bit is set to 1, while
lower link rate when all CR DONE bits are 0s. However in our code, we will
treat both cases as latter. This is not exactly correct based on the specs
expectation.

[how]
Check lane0 CR DONE bit when it is still set but CR DONE fails,
we treat it as a partial CR DONE failure in EQ DONE phase, we
will follow the same fallback flow as when ED DONE fails in EQ
DONE phase.

Reviewed-by: George Shen <George.Shen@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/gpu/drm/amd/display/include/link_service_types.h b/drivers/gpu/drm/amd/display/include/link_service_types.h
index 447a56286dd0..23f7d7354aaa 100644
--- a/drivers/gpu/drm/amd/display/include/link_service_types.h
+++ b/drivers/gpu/drm/amd/display/include/link_service_types.h
@@ -67,6 +67,8 @@ enum link_training_result {
 	LINK_TRAINING_CR_FAIL_LANE23,
 	/* CR DONE bit is cleared during EQ step */
 	LINK_TRAINING_EQ_FAIL_CR,
+	/* CR DONE bit is cleared but LANE0_CR_DONE is set during EQ step */
+	LINK_TRAINING_EQ_FAIL_CR_PARTIAL,
 	/* other failure during EQ step */
 	LINK_TRAINING_EQ_FAIL_EQ,
 	LINK_TRAINING_LQA_FAIL,