[Intel-gfx] [PATCH v2 3/4] drm/i915: Find fallback link rate/lane count

[Manasi Navare]

If link training fails, then we need to fallback to lower
link rate first and if link training fails at RBR, then
fallback to lower lane count.
This function finds the next lower link rate/lane count
value after link training failure.

v2:
Squash the patch that returns the link rate index (Jani Nikula)

Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Daniel Vetter <daniel.vetter at intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c  | 43 ++++++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_drv.h |  6 ++++++
 2 files changed, 49 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 2b6f51c..fb4fcdd 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -288,6 +288,49 @@ static int intel_dp_common_rates(struct intel_dp *intel_dp,
 			       common_rates);
 }
 
+static int intel_dp_link_rate_index(struct intel_dp *intel_dp,
+				    int *common_rates, int link_rate)
+{
+	int common_len;
+	int index;
+
+	common_len = intel_dp_common_rates(intel_dp, common_rates);
+	for (index = 0; index < common_len; index++) {
+		if (link_rate == common_rates[common_len - index - 1])
+			return common_len - index - 1;
+	}
+
+	return -1;
+}
+
+void intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
+					     int link_rate, uint8_t lane_count)
+{
+	int common_rates[DP_MAX_SUPPORTED_RATES] = {};
+	int common_len;
+	int link_rate_index = -1;
+
+	if (!intel_dp->link_train_failed)
+		return;
+
+	common_len = intel_dp_common_rates(intel_dp, common_rates);
+	link_rate_index = intel_dp_link_rate_index(intel_dp,
+						   common_rates,
+						   link_rate);
+	if (link_rate_index > 0) {
+		intel_dp->fallback_link_rate_index = link_rate_index - 1;
+		intel_dp->fallback_link_rate = common_rates[intel_dp->fallback_link_rate_index];
+		intel_dp->fallback_lane_count = intel_dp_max_lane_count(intel_dp);
+	} else if (lane_count > 1) {
+		intel_dp->fallback_link_rate_index = common_len - 1;
+		intel_dp->fallback_link_rate = common_rates[intel_dp->fallback_link_rate_index];
+		intel_dp->fallback_lane_count = lane_count >> 1;
+	} else {
+		DRM_ERROR("Link Training Unsuccessful\n");
+		intel_dp->link_train_failed = false;
+	}
+}
+
 static enum drm_mode_status
 intel_dp_mode_valid(struct drm_connector *connector,
 		    struct drm_display_mode *mode)
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 3cb7481..bc25b2b 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -897,6 +897,10 @@ struct intel_dp {
 	uint32_t DP;
 	int link_rate;
 	uint8_t lane_count;
+	int fallback_link_rate;
+	uint8_t fallback_lane_count;
+	int fallback_link_rate_index;
+	bool link_train_failed;
 	uint8_t sink_count;
 	bool link_mst;
 	bool has_audio;
@@ -1396,6 +1400,8 @@ int intel_dp_set_link_status_property(struct drm_connector *connector,
 void intel_dp_set_link_params(struct intel_dp *intel_dp,
 			      int link_rate, uint8_t lane_count,
 			      bool link_mst);
+void intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
+					     int link_rate, uint8_t lane_count);
 void intel_dp_start_link_train(struct intel_dp *intel_dp);
 void intel_dp_stop_link_train(struct intel_dp *intel_dp);
 void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode);
-- 
1.9.1