Re: [PATCH] Revert "drm/i915/edp: Do not do link training fallback or prune modes on EDP"

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 16 May 2018, Lucas De Marchi <lucas.demarchi@intel.com> wrote:
> This reverts commit c0cfb10d9e1de490e36d3b9d4228c0ea0ca30677.
>
> This fails on a Dell XPS13 9350 machine giving me just a black screen.
>  [drm:intel_dp_start_link_train [i915]] [CONNECTOR:59:eDP-1] Link Training Passed at Link Rate = 540000, Lane count = 4
>  [drm:intel_dp_start_link_train [i915]] *ERROR* [CONNECTOR:59:eDP-1] Link Training failed at link rate = 540000, lane count = 4
>  [drm:intel_dp_start_link_train [i915]] [CONNECTOR:59:eDP-1] Link Training Passed at Link Rate = 540000, Lane count = 4
>  [drm:intel_dp_start_link_train [i915]] [CONNECTOR:59:eDP-1] Link Training Passed at Link Rate = 540000, Lane count = 4
>  [drm:intel_dp_start_link_train [i915]] [CONNECTOR:59:eDP-1] Link Training Passed at Link Rate = 540000, Lane count = 4
>  [drm:intel_dp_start_link_train [i915]] *ERROR* [CONNECTOR:59:eDP-1] Link Training failed at link rate = 540000, lane count = 4
>  [drm:intel_dp_start_link_train [i915]] *ERROR* [CONNECTOR:59:eDP-1] Link Training failed at link rate = 540000, lane count = 4
>  [drm:intel_dp_start_link_train [i915]] [CONNECTOR:59:eDP-1] Link Training Passed at Link Rate = 540000, Lane count = 4
>  [drm:intel_dp_start_link_train [i915]] *ERROR* [CONNECTOR:59:eDP-1] Link Training failed at link rate = 540000, lane count = 4
>  [drm:intel_dp_start_link_train [i915]] [CONNECTOR:59:eDP-1] Link Training Passed at Link Rate = 540000, Lane count = 4
>  [drm:intel_dp_start_link_train [i915]] [CONNECTOR:59:eDP-1] Link Training Passed at Link Rate = 540000, Lane count = 4
>  [drm:intel_dp_start_link_train [i915]] *ERROR* [CONNECTOR:59:eDP-1] Link Training failed at link rate = 540000, lane count = 4
>
> On a working kernel, previous to this commit I have:
>  [drm:intel_dp_start_link_train [i915]] [CONNECTOR:59:eDP-1] Link Training failed at link rate = 540000, lane count = 4
>  [drm:intel_dp_start_link_train [i915]] [CONNECTOR:59:eDP-1] Link Training Passed at Link Rate = 270000, Lane count = 4

We had this kind of issues *before* any link fallback, way back when we
just plunged on ignoring issues. Actually I imagined we were going to do
that for eDP when c0cfb10d9e1d ("drm/i915/edp: Do not do link training
fallback or prune modes on EDP") was introduced, but looks like we
don't.

Does this work? It might not, because way back we used to have a full
clock recovery step within channel eq error path, and that then worked
just fine.

BR,
Jani.

diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
index 3fcaa98b9055..7315ee01f984 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -323,7 +323,8 @@ intel_dp_start_link_train(struct intel_dp *intel_dp)
 {
 	struct intel_connector *intel_connector = intel_dp->attached_connector;
 
-	if (!intel_dp_link_training_clock_recovery(intel_dp))
+	if (!intel_dp_link_training_clock_recovery(intel_dp) &&
+	    !intel_dp_is_edp(intel_dp))
 		goto failure_handling;
 	if (!intel_dp_link_training_channel_equalization(intel_dp))
 		goto failure_handling;



-- 
Jani Nikula, Intel Open Source Graphics Center
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