Merge tag 'backlight-next-5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight

Pull backlight updates from Lee Jones:
 "New Functionality:
   - Provide support for ACPI enumeration; gpio_backlight

  Fix-ups:
   - SPDX fixups; pwm_bl
   - Fix linear	brightness levels to include number available; pwm_bl"

* tag 'backlight-next-5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight:
  backlight: pwm_bl: Fix heuristic to determine number of brightness levels
  backlight: gpio_backlight: Enable ACPI enumeration
  backlight: pwm_bl: Convert to use SPDX identifier

drivers/video/backlight/gpio_backlight.c

@@ -15,6 +15,7 @@
 #include <linux/of_gpio.h>
 #include <linux/platform_data/gpio_backlight.h>
 #include <linux/platform_device.h>
+#include <linux/property.h>
 #include <linux/slab.h>
 
 struct gpio_backlight {
@@ -58,11 +59,10 @@ static int gpio_backlight_probe_dt(struct platform_device *pdev,
 				   struct gpio_backlight *gbl)
 {
 	struct device *dev = &pdev->dev;
-	struct device_node *np = dev->of_node;
 	enum gpiod_flags flags;
 	int ret;
 
-	gbl->def_value = of_property_read_bool(np, "default-on");
+	gbl->def_value = device_property_read_bool(dev, "default-on");
 	flags = gbl->def_value ? GPIOD_OUT_HIGH : GPIOD_OUT_LOW;
 
 	gbl->gpiod = devm_gpiod_get(dev, NULL, flags);
@@ -86,26 +86,19 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 	struct backlight_properties props;
 	struct backlight_device *bl;
 	struct gpio_backlight *gbl;
-	struct device_node *np = pdev->dev.of_node;
 	int ret;
 
-	if (!pdata && !np) {
-		dev_err(&pdev->dev,
-			"failed to find platform data or device tree node.\n");
-		return -ENODEV;
-	}
-
 	gbl = devm_kzalloc(&pdev->dev, sizeof(*gbl), GFP_KERNEL);
 	if (gbl == NULL)
 		return -ENOMEM;
 
 	gbl->dev = &pdev->dev;
 
-	if (np) {
+	if (pdev->dev.fwnode) {
 		ret = gpio_backlight_probe_dt(pdev, gbl);
 		if (ret)
 			return ret;
-	} else {
+	} else if (pdata) {
 		/*
 		 * Legacy platform data GPIO retrieveal. Do not expand
 		 * the use of this code path, currently only used by one
@@ -126,6 +119,10 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 		gbl->gpiod = gpio_to_desc(pdata->gpio);
 		if (!gbl->gpiod)
 			return -EINVAL;
+	} else {
+		dev_err(&pdev->dev,
+			"failed to find platform data or device tree node.\n");
+		return -ENODEV;
 	}
 
 	memset(&props, 0, sizeof(props));
@@ -146,19 +143,17 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 	return 0;
 }
 
-#ifdef CONFIG_OF
 static struct of_device_id gpio_backlight_of_match[] = {
 	{ .compatible = "gpio-backlight" },
 	{ /* sentinel */ }
 };
 
 MODULE_DEVICE_TABLE(of, gpio_backlight_of_match);
-#endif
 
 static struct platform_driver gpio_backlight_driver = {
 	.driver		= {
 		.name		= "gpio-backlight",
-		.of_match_table = of_match_ptr(gpio_backlight_of_match),
+		.of_match_table = gpio_backlight_of_match,
 	},
 	.probe		= gpio_backlight_probe,
 };

drivers/video/backlight/pwm_bl.c

 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * linux/drivers/video/backlight/pwm_bl.c
- *
- * simple PWM based backlight control, board code has to setup
+ * Simple PWM based backlight control, board code has to setup
  * 1) pin configuration so PWM waveforms can output
  * 2) platform_data being correctly configured
  */
@@ -191,29 +189,17 @@ int pwm_backlight_brightness_default(struct device *dev,
 				     struct platform_pwm_backlight_data *data,
 				     unsigned int period)
 {
-	unsigned int counter = 0;
-	unsigned int i, n;
+	unsigned int i;
 	u64 retval;
 
 	/*
-	 * Count the number of bits needed to represent the period number. The
-	 * number of bits is used to calculate the number of levels used for the
-	 * brightness-levels table, the purpose of this calculation is have a
-	 * pre-computed table with enough levels to get linear brightness
-	 * perception. The period is divided by the number of bits so for a
-	 * 8-bit PWM we have 255 / 8 = 32 brightness levels or for a 16-bit PWM
-	 * we have 65535 / 16 = 4096 brightness levels.
-	 *
-	 * Note that this method is based on empirical testing on different
-	 * devices with PWM of 8 and 16 bits of resolution.
+	 * Once we have 4096 levels there's little point going much higher...
+	 * neither interactive sliders nor animation benefits from having
+	 * more values in the table.
 	 */
-	n = period;
-	while (n) {
-		counter += n % 2;
-		n >>= 1;
-	}
+	data->max_brightness =
+		min((int)DIV_ROUND_UP(period, fls(period)), 4096);
 
-	data->max_brightness = DIV_ROUND_UP(period, counter);
 	data->levels = devm_kcalloc(dev, data->max_brightness,
 				    sizeof(*data->levels), GFP_KERNEL);
 	if (!data->levels)
@@ -705,5 +691,5 @@ static struct platform_driver pwm_backlight_driver = {
 module_platform_driver(pwm_backlight_driver);
 
 MODULE_DESCRIPTION("PWM based Backlight Driver");
-MODULE_LICENSE("GPL");
+MODULE_LICENSE("GPL v2");
 MODULE_ALIAS("platform:pwm-backlight");