drm/panel: tpo-td028ttec1: use drm_panel backlight support

Use the backlight support in drm_panel to simplify the driver
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191207140353.23967-25-sam@ravnborg.org

drivers/gpu/drm/panel/panel-tpo-td028ttec1.c

@@ -17,7 +17,6 @@
  * H. Nikolaus Schaller <hns@goldelico.com>
  */
 
-#include <linux/backlight.h>
 #include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/spi/spi.h>
@@ -83,7 +82,6 @@ struct td028ttec1_panel {
 	struct drm_panel panel;
 
 	struct spi_device *spi;
-	struct backlight_device *backlight;
 };
 
 #define to_td028ttec1_device(p) container_of(p, struct td028ttec1_panel, panel)
@@ -243,8 +241,6 @@ static int td028ttec1_enable(struct drm_panel *panel)
 	if (ret)
 		return ret;
 
-	backlight_enable(lcd->backlight);
-
 	return 0;
 }
 
@@ -252,8 +248,6 @@ static int td028ttec1_disable(struct drm_panel *panel)
 {
 	struct td028ttec1_panel *lcd = to_td028ttec1_device(panel);
 
-	backlight_disable(lcd->backlight);
-
 	jbt_ret_write_0(lcd, JBT_REG_DISPLAY_OFF, NULL);
 
 	return 0;
@@ -334,10 +328,6 @@ static int td028ttec1_probe(struct spi_device *spi)
 	spi_set_drvdata(spi, lcd);
 	lcd->spi = spi;
 
-	lcd->backlight = devm_of_find_backlight(&spi->dev);
-	if (IS_ERR(lcd->backlight))
-		return PTR_ERR(lcd->backlight);
-
 	spi->mode = SPI_MODE_3;
 	spi->bits_per_word = 9;
 
@@ -350,6 +340,10 @@ static int td028ttec1_probe(struct spi_device *spi)
 	drm_panel_init(&lcd->panel, &lcd->spi->dev, &td028ttec1_funcs,
 		       DRM_MODE_CONNECTOR_DPI);
 
+	ret = drm_panel_of_backlight(&lcd->panel);
+	if (ret)
+		return ret;
+
 	return drm_panel_add(&lcd->panel);
 }