drm/amd/display/amdgpu_dm: Refactor register_backlight_device()

Refactor register_backlight_device():

1) Turn the connector-type + signal check into an early exit
condition to avoid the indentation level of the rest of the code

2) Add an array bounds check for the arrays indexed by dm->num_of_edps

3) register_backlight_device() always increases dm->num_of_edps if
amdgpu_dm_register_backlight_device() has assigned a backlight_dev to
the current dm->backlight_link[dm->num_of_edps] slot.

So on its next call dm->backlight_dev[dm->num_of_edps] always point to
the next empty slot and the "if (!dm->backlight_dev[dm->num_of_edps])"
check will thus always succeed and can be removed.

4) Add a bl_idx local variable to use as array index, rather then
using dm->num_of_edps to improve the code readability.
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -4269,21 +4269,23 @@ static int initialize_plane(struct amdgpu_display_manager *dm,
 static void register_backlight_device(struct amdgpu_display_manager *dm,
 				      struct dc_link *link)
 {
-	if ((link->connector_signal & (SIGNAL_TYPE_EDP | SIGNAL_TYPE_LVDS)) &&
-	    link->type != dc_connection_none) {
-		/*
-		 * Event if registration failed, we should continue with
-		 * DM initialization because not having a backlight control
-		 * is better then a black screen.
-		 */
-		if (!dm->backlight_dev[dm->num_of_edps])
-			amdgpu_dm_register_backlight_device(dm);
+	int bl_idx = dm->num_of_edps;
 
-		if (dm->backlight_dev[dm->num_of_edps]) {
-			dm->backlight_link[dm->num_of_edps] = link;
-			dm->num_of_edps++;
-		}
+	if (!(link->connector_signal & (SIGNAL_TYPE_EDP | SIGNAL_TYPE_LVDS)) ||
+	    link->type == dc_connection_none)
+		return;
+
+	if (dm->num_of_edps >= AMDGPU_DM_MAX_NUM_EDP) {
+		drm_warn(adev_to_drm(dm->adev), "Too much eDP connections, skipping backlight setup for additional eDPs\n");
+		return;
 	}
+
+	amdgpu_dm_register_backlight_device(dm);
+	if (!dm->backlight_dev[bl_idx])
+		return;
+
+	dm->backlight_link[bl_idx] = link;
+	dm->num_of_edps++;
 }
 
 static void amdgpu_set_panel_orientation(struct drm_connector *connector);