[PATCH 2/3] 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 and limits the max
link_rate and lane_count values to these fallback values.

v6:
* Cap the max link rate and lane count to the max
values obtained during fallback link training (Daniel Vetter)
v5:
* Start the fallback at the lane count value passed not
the max lane count (Jani Nikula)
v4:
* Remove the redundant variable link_train_failed
v3:
* Remove fallback_link_rate_index variable, just obtain
that using the helper intel_dp_link_rate_index (Jani Nikula)
v2:
Squash the patch that returns the link rate index (Jani Nikula)

Acked-by: Tony Cheng <tony.cheng at amd.com>
Acked-by: Harry Wentland <harry.wentland at amd.com>
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  | 59 ++++++++++++++++++++++++++++++++++++++--
 drivers/gpu/drm/i915/intel_drv.h |  4 +++
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 8026a83..bc1268c 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -153,12 +153,18 @@ static void vlv_steal_power_sequencer(struct drm_device *dev,
 static u8 intel_dp_max_lane_count(struct intel_dp *intel_dp)
 {
 	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
-	u8 source_max, sink_max;
+	u8 temp, source_max, sink_max;
 
 	source_max = intel_dig_port->max_lanes;
 	sink_max = drm_dp_max_lane_count(intel_dp->dpcd);
+	temp = min(source_max, sink_max);
+	/* Limit the max value to max fallback value during link train
+	 * failure handling.
+	 */
+	if (intel_dp->fallback_lane_count)
+		return min(temp, intel_dp->fallback_lane_count);
 
-	return min(source_max, sink_max);
+	return temp;
 }
 
 /*
@@ -281,6 +287,15 @@ static int intel_dp_common_rates(struct intel_dp *intel_dp,
 	int source_len, sink_len;
 
 	sink_len = intel_dp_sink_rates(intel_dp, &sink_rates);
+	/* Limit the max sink rate to the max fallback link rate
+	 * found during link training failure handling.
+	 */
+	if (intel_dp->fallback_link_rate) {
+		int len = sink_len - 1;
+		while (len > 0 && sink_rates[len] > intel_dp->fallback_link_rate)
+			len--;
+		sink_len = len + 1;
+	}
 	source_len = intel_dp_source_rates(intel_dp, &source_rates);
 
 	return intersect_rates(source_rates, source_len,
@@ -288,6 +303,46 @@ 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;
+}
+
+int 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;
+
+	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 = common_rates[link_rate_index - 1];
+		intel_dp->fallback_lane_count = lane_count;
+	} else if (lane_count > 1) {
+		intel_dp->fallback_link_rate = 0;
+		intel_dp->fallback_lane_count = lane_count >> 1;
+	} else {
+		DRM_ERROR("Link Training Unsuccessful\n");
+		return -1;
+	}
+
+	return 0;
+}
+
 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 9bbe5c5..2da3b40 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -891,6 +891,8 @@ struct intel_dp {
 	uint32_t DP;
 	int link_rate;
 	uint8_t lane_count;
+	int fallback_link_rate;
+	uint8_t fallback_lane_count;
 	uint8_t sink_count;
 	bool link_mst;
 	bool has_audio;
@@ -1393,6 +1395,8 @@ bool intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
 void intel_dp_set_link_params(struct intel_dp *intel_dp,
 			      int link_rate, uint8_t lane_count,
 			      bool link_mst);
+int 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