drm/i915/dp: Add debugfs entries to get the max link rate/lane count

Add connector debugfs entries to get the maximum link rate and lane
count.

v2: Lock connection_mutex only for the required intel_dp state. (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240610164933.2947366-19-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_dp_link_training.c

@@ -1770,6 +1770,44 @@ static ssize_t i915_dp_force_lane_count_write(struct file *file,
 }
 DEFINE_SHOW_STORE_ATTRIBUTE(i915_dp_force_lane_count);
 
+static int i915_dp_max_link_rate_show(void *data, u64 *val)
+{
+	struct intel_connector *connector = to_intel_connector(data);
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = intel_connector_to_intel_dp(connector);
+	int err;
+
+	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
+	if (err)
+		return err;
+
+	*val = intel_dp->link.max_rate;
+
+	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
+
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(i915_dp_max_link_rate_fops, i915_dp_max_link_rate_show, NULL, "%llu\n");
+
+static int i915_dp_max_lane_count_show(void *data, u64 *val)
+{
+	struct intel_connector *connector = to_intel_connector(data);
+	struct drm_i915_private *i915 = to_i915(connector->base.dev);
+	struct intel_dp *intel_dp = intel_connector_to_intel_dp(connector);
+	int err;
+
+	err = drm_modeset_lock_single_interruptible(&i915->drm.mode_config.connection_mutex);
+	if (err)
+		return err;
+
+	*val = intel_dp->link.max_lane_count;
+
+	drm_modeset_unlock(&i915->drm.mode_config.connection_mutex);
+
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(i915_dp_max_lane_count_fops, i915_dp_max_lane_count_show, NULL, "%llu\n");
+
 void intel_dp_link_training_debugfs_add(struct intel_connector *connector)
 {
 	struct dentry *root = connector->base.debugfs_entry;
@@ -1783,4 +1821,10 @@ void intel_dp_link_training_debugfs_add(struct intel_connector *connector)
 
 	debugfs_create_file("i915_dp_force_lane_count", 0644, root,
 			    connector, &i915_dp_force_lane_count_fops);
+
+	debugfs_create_file("i915_dp_max_link_rate", 0444, root,
+			    connector, &i915_dp_max_link_rate_fops);
+
+	debugfs_create_file("i915_dp_max_lane_count", 0444, root,
+			    connector, &i915_dp_max_lane_count_fops);
 }