[PATCH] drm/i915: Make DP fast link training a module parameter

[Mika Kahola <mika.kahola@intel.com>]

There is a bug report

https://bugs.freedesktop.org/show_bug.cgi?id=91393

indicating that there are panels that do not support
link training starting with non-zero voltage swing and
pre-emphasis values.

This patch proposes to make this fast link training
feature as one module parameter. To take more conservative
approach this feature is disabled by default.

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h               |  1 +
 drivers/gpu/drm/i915/i915_params.c            |  4 ++++
 drivers/gpu/drm/i915/intel_dp_link_training.c | 11 ++++++++++-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index a47e0f4..dc2d5a0 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2669,6 +2669,7 @@ struct i915_params {
 	bool verbose_state_checks;
 	bool nuclear_pageflip;
 	int edp_vswing;
+	bool enable_dp_flt;
 };
 extern struct i915_params i915 __read_mostly;
 
diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index 835d609..aea5d47 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -56,6 +56,7 @@ struct i915_params i915 __read_mostly = {
 	.edp_vswing = 0,
 	.enable_guc_submission = false,
 	.guc_log_level = -1,
+	.enable_dp_flt = false,
 };
 
 module_param_named(modeset, i915.modeset, int, 0400);
@@ -202,3 +203,6 @@ MODULE_PARM_DESC(enable_guc_submission, "Enable GuC submission (default:false)")
 module_param_named(guc_log_level, i915.guc_log_level, int, 0400);
 MODULE_PARM_DESC(guc_log_level,
 	"GuC firmware logging level (-1:disabled (default), 0-3:enabled)");
+
+module_param_named_unsafe(enable_dp_flt, i915.enable_dp_flt, bool, 0400);
+MODULE_PARM_DESC(enable_dp_flt, "Enable DP fast link training (default:false)");
diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
index 8888793..f8b6d69 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -85,8 +85,17 @@ static bool
 intel_dp_reset_link_train(struct intel_dp *intel_dp,
 			uint8_t dp_train_pat)
 {
-	if (!intel_dp->train_set_valid)
+	if (i915.enable_dp_flt) {
+		DRM_DEBUG_KMS("DP flt enabled, train set valid: %s\n",
+			      intel_dp->train_set_valid ? "true" : "false");
+
+		if (!intel_dp->train_set_valid)
+			memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
+	} else {
+		DRM_DEBUG_KMS("DP flt disabled\n");
 		memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
+	}
+
 	intel_dp_set_signal_levels(intel_dp);
 	return intel_dp_set_link_train(intel_dp, dp_train_pat);
 }
-- 
1.9.1

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