backlight: add led-backlight driver

This patch adds a led-backlight driver (led_bl), which is similar to
pwm_bl except the driver uses a LED class driver to adjust the
brightness in the HW. Multiple LEDs can be used for a single backlight.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Tony Lindgren <tony@atomide.com>

drivers/video/backlight/Kconfig

@@ -456,6 +456,13 @@ config BACKLIGHT_RAVE_SP
 	help
 	  Support for backlight control on RAVE SP device.
 
+config BACKLIGHT_LED
+	tristate "Generic LED based Backlight Driver"
+	depends on LEDS_CLASS && OF
+	help
+	  If you have a LCD backlight adjustable by LED class driver, say Y
+	  to enable this driver.
+
 endif # BACKLIGHT_CLASS_DEVICE
 
 endmenu

drivers/video/backlight/Makefile

@@ -57,3 +57,4 @@ obj-$(CONFIG_BACKLIGHT_TPS65217)	+= tps65217_bl.o
 obj-$(CONFIG_BACKLIGHT_WM831X)		+= wm831x_bl.o
 obj-$(CONFIG_BACKLIGHT_ARCXCNN) 	+= arcxcnn_bl.o
 obj-$(CONFIG_BACKLIGHT_RAVE_SP)		+= rave-sp-backlight.o
+obj-$(CONFIG_BACKLIGHT_LED)		+= led_bl.o

drivers/video/backlight/led_bl.c

@@ -0,0 +1,260 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015-2019 Texas Instruments Incorporated -  http://www.ti.com/
+ * Author: Tomi Valkeinen <tomi.valkeinen@ti.com>
+ *
+ * Based on pwm_bl.c
+ */
+
+#include <linux/backlight.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+struct led_bl_data {
+	struct device		*dev;
+	struct backlight_device	*bl_dev;
+	struct led_classdev	**leds;
+	bool			enabled;
+	int			nb_leds;
+	unsigned int		*levels;
+	unsigned int		default_brightness;
+	unsigned int		max_brightness;
+};
+
+static void led_bl_set_brightness(struct led_bl_data *priv, int level)
+{
+	int i;
+	int bkl_brightness;
+
+	if (priv->levels)
+		bkl_brightness = priv->levels[level];
+	else
+		bkl_brightness = level;
+
+	for (i = 0; i < priv->nb_leds; i++)
+		led_set_brightness(priv->leds[i], bkl_brightness);
+
+	priv->enabled = true;
+}
+
+static void led_bl_power_off(struct led_bl_data *priv)
+{
+	int i;
+
+	if (!priv->enabled)
+		return;
+
+	for (i = 0; i < priv->nb_leds; i++)
+		led_set_brightness(priv->leds[i], LED_OFF);
+
+	priv->enabled = false;
+}
+
+static int led_bl_update_status(struct backlight_device *bl)
+{
+	struct led_bl_data *priv = bl_get_data(bl);
+	int brightness = bl->props.brightness;
+
+	if (bl->props.power != FB_BLANK_UNBLANK ||
+	    bl->props.fb_blank != FB_BLANK_UNBLANK ||
+	    bl->props.state & BL_CORE_FBBLANK)
+		brightness = 0;
+
+	if (brightness > 0)
+		led_bl_set_brightness(priv, brightness);
+	else
+		led_bl_power_off(priv);
+
+	return 0;
+}
+
+static const struct backlight_ops led_bl_ops = {
+	.update_status	= led_bl_update_status,
+};
+
+static int led_bl_get_leds(struct device *dev,
+			   struct led_bl_data *priv)
+{
+	int i, nb_leds, ret;
+	struct device_node *node = dev->of_node;
+	struct led_classdev **leds;
+	unsigned int max_brightness;
+	unsigned int default_brightness;
+
+	ret = of_count_phandle_with_args(node, "leds", NULL);
+	if (ret < 0) {
+		dev_err(dev, "Unable to get led count\n");
+		return -EINVAL;
+	}
+
+	nb_leds = ret;
+	if (nb_leds < 1) {
+		dev_err(dev, "At least one LED must be specified!\n");
+		return -EINVAL;
+	}
+
+	leds = devm_kzalloc(dev, sizeof(struct led_classdev *) * nb_leds,
+			    GFP_KERNEL);
+	if (!leds)
+		return -ENOMEM;
+
+	for (i = 0; i < nb_leds; i++) {
+		leds[i] = devm_of_led_get(dev, i);
+		if (IS_ERR(leds[i]))
+			return PTR_ERR(leds[i]);
+	}
+
+	/* check that the LEDs all have the same brightness range */
+	max_brightness = leds[0]->max_brightness;
+	for (i = 1; i < nb_leds; i++) {
+		if (max_brightness != leds[i]->max_brightness) {
+			dev_err(dev, "LEDs must have identical ranges\n");
+			return -EINVAL;
+		}
+	}
+
+	/* get the default brightness from the first LED from the list */
+	default_brightness = leds[0]->brightness;
+
+	priv->nb_leds = nb_leds;
+	priv->leds = leds;
+	priv->max_brightness = max_brightness;
+	priv->default_brightness = default_brightness;
+
+	return 0;
+}
+
+static int led_bl_parse_levels(struct device *dev,
+			   struct led_bl_data *priv)
+{
+	struct device_node *node = dev->of_node;
+	int num_levels;
+	u32 value;
+	int ret;
+
+	if (!node)
+		return -ENODEV;
+
+	num_levels = of_property_count_u32_elems(node, "brightness-levels");
+	if (num_levels > 1) {
+		int i;
+		unsigned int db;
+		u32 *levels = NULL;
+
+		levels = devm_kzalloc(dev, sizeof(u32) * num_levels,
+				      GFP_KERNEL);
+		if (!levels)
+			return -ENOMEM;
+
+		ret = of_property_read_u32_array(node, "brightness-levels",
+						levels,
+						num_levels);
+		if (ret < 0)
+			return ret;
+
+		/*
+		 * Try to map actual LED brightness to backlight brightness
+		 * level
+		 */
+		db = priv->default_brightness;
+		for (i = 0 ; i < num_levels; i++) {
+			if ((i && db > levels[i-1]) && db <= levels[i])
+				break;
+		}
+		priv->default_brightness = i;
+		priv->max_brightness = num_levels - 1;
+		priv->levels = levels;
+	} else if (num_levels >= 0)
+		dev_warn(dev, "Not enough levels defined\n");
+
+	ret = of_property_read_u32(node, "default-brightness-level", &value);
+	if (!ret && value <= priv->max_brightness)
+		priv->default_brightness = value;
+	else if (!ret  && value > priv->max_brightness)
+		dev_warn(dev, "Invalid default brightness. Ignoring it\n");
+
+	return 0;
+}
+
+static int led_bl_probe(struct platform_device *pdev)
+{
+	struct backlight_properties props;
+	struct led_bl_data *priv;
+	int ret, i;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, priv);
+
+	priv->dev = &pdev->dev;
+
+	ret = led_bl_get_leds(&pdev->dev, priv);
+	if (ret)
+		return ret;
+
+	ret = led_bl_parse_levels(&pdev->dev, priv);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "Failed to parse DT data\n");
+		return ret;
+	}
+
+	memset(&props, 0, sizeof(struct backlight_properties));
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = priv->max_brightness;
+	props.brightness = priv->default_brightness;
+	props.power = (priv->default_brightness > 0) ? FB_BLANK_POWERDOWN :
+		      FB_BLANK_UNBLANK;
+	priv->bl_dev = backlight_device_register(dev_name(&pdev->dev),
+			&pdev->dev, priv, &led_bl_ops, &props);
+	if (IS_ERR(priv->bl_dev)) {
+		dev_err(&pdev->dev, "Failed to register backlight\n");
+		return PTR_ERR(priv->bl_dev);
+	}
+
+	for (i = 0; i < priv->nb_leds; i++)
+		led_sysfs_disable(priv->leds[i]);
+
+	backlight_update_status(priv->bl_dev);
+
+	return 0;
+}
+
+static int led_bl_remove(struct platform_device *pdev)
+{
+	struct led_bl_data *priv = platform_get_drvdata(pdev);
+	struct backlight_device *bl = priv->bl_dev;
+	int i;
+
+	backlight_device_unregister(bl);
+
+	led_bl_power_off(priv);
+	for (i = 0; i < priv->nb_leds; i++)
+		led_sysfs_enable(priv->leds[i]);
+
+	return 0;
+}
+
+static const struct of_device_id led_bl_of_match[] = {
+	{ .compatible = "led-backlight" },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(of, led_bl_of_match);
+
+static struct platform_driver led_bl_driver = {
+	.driver		= {
+		.name		= "led-backlight",
+		.of_match_table	= of_match_ptr(led_bl_of_match),
+	},
+	.probe		= led_bl_probe,
+	.remove		= led_bl_remove,
+};
+
+module_platform_driver(led_bl_driver);
+
+MODULE_DESCRIPTION("LED based Backlight Driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:led-backlight");