drm/omap: panel-tpo-td028ttec1: add backlight support

This panel has a backlight, so fetch it from devicetree using the
corresponding property as documented in panel-common.txt. It is
implemented the same way as in panel-dpi.c
This ensures the backlight is also disabled when the display is
turned off like when doing xset dpms force off.
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

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

@@ -35,6 +35,8 @@ struct panel_drv_data {
 
 	struct videomode vm;
 
+	struct backlight_device *backlight;
+
 	struct spi_device *spi_dev;
 };
 
@@ -258,12 +260,16 @@ static void td028ttec1_panel_enable(struct omap_dss_device *dssdev)
 
 	if (r)
 		dev_err(dssdev->dev, "%s: write error\n", __func__);
+
+	backlight_enable(ddata->backlight);
 }
 
 static void td028ttec1_panel_disable(struct omap_dss_device *dssdev)
 {
 	struct panel_drv_data *ddata = to_panel_data(dssdev);
 
+	backlight_disable(ddata->backlight);
+
 	dev_dbg(dssdev->dev, "td028ttec1_panel_disable()\n");
 
 	jbt_ret_write_0(ddata, JBT_REG_DISPLAY_OFF);
@@ -311,6 +317,10 @@ static int td028ttec1_panel_probe(struct spi_device *spi)
 	if (ddata == NULL)
 		return -ENOMEM;
 
+	ddata->backlight = devm_of_find_backlight(&spi->dev);
+	if (IS_ERR(ddata->backlight))
+		return PTR_ERR(ddata->backlight);
+
 	dev_set_drvdata(&spi->dev, ddata);
 
 	ddata->spi_dev = spi;