- Core Frameworks

- Obtain scale type through sysfs
 
  - New Functionality
    - Provide Device Tree functionality; rave-sp-backlight
    - Calculate if scale type is (non-)linear; pwm_bl
 
  - Fix-ups
    - Simplify code; lm3630a_bl
    - Trivial rename/whitespace/typo fixes; lms283gf05
    - Remove superfluous NULL check; tosa_lcd
    - Fix power state initialisation; gpio_backlight
    - List supported file; MAINTAINERS
 
  - Bug Fixes
    - Kconfig - default to not building unless requested; {LED,BACKLIGHT}_CLASS_DEVICE
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Merge tag 'backlight-next-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight

Pull backlight updates from Lee Jones:
 "Core Frameworks
   - Obtain scale type through sysfs

  New Functionality:
   - Provide Device Tree functionality in rave-sp-backlight
   - Calculate if scale type is (non-)linear in pwm_bl

  Fix-ups:
   - Simplify code in lm3630a_bl
   - Trivial rename/whitespace/typo fixes in lms283gf05
   - Remove superfluous NULL check in tosa_lcd
   - Fix power state initialisation in gpio_backlight
   - List supported file in MAINTAINERS

  Bug Fixes:
   - Kconfig - default to not building unless requested in
     {LED,BACKLIGHT}_CLASS_DEVICE"

* tag 'backlight-next-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight:
  backlight: pwm_bl: Set scale type for brightness curves specified in the DT
  backlight: pwm_bl: Set scale type for CIE 1931 curves
  backlight: Expose brightness curve type through sysfs
  MAINTAINERS: Add entry for stable backlight sysfs ABI documentation
  backlight: gpio-backlight: Correct initial power state handling
  video: backlight: tosa_lcd: drop check because i2c_unregister_device() is NULL safe
  video: backlight: Drop default m for {LCD,BACKLIGHT_CLASS_DEVICE}
  backlight: lms283gf05: Fix a typo in the description passed to 'devm_gpio_request_one()'
  backlight: lm3630a: Switch to use fwnode_property_count_uXX()
  backlight: rave-sp: Leave initial state and register with correct device

Documentation/ABI/testing/sysfs-class-backlight

@@ -0,0 +1,26 @@
+What:		/sys/class/backlight/<backlight>/scale
+Date:		July 2019
+KernelVersion:	5.4
+Contact:	Daniel Thompson <daniel.thompson@linaro.org>
+Description:
+		Description of the scale of the brightness curve.
+
+		The human eye senses brightness approximately logarithmically,
+		hence linear changes in brightness are perceived as being
+		non-linear. To achieve a linear perception of brightness changes
+		controls like sliders need to apply a logarithmic mapping for
+		backlights with a linear brightness curve.
+
+		Possible values of the attribute are:
+
+		unknown
+		  The scale of the brightness curve is unknown.
+
+		linear
+		  The brightness changes linearly with each step. Brightness
+		  controls should apply a logarithmic mapping for a linear
+		  perception.
+
+		non-linear
+		  The brightness changes non-linearly with each step. Brightness
+		  controls should use a linear mapping for a linear perception.

MAINTAINERS

@@ -2921,6 +2921,8 @@ F:	drivers/video/backlight/
 F:	include/linux/backlight.h
 F:	include/linux/pwm_backlight.h
 F:	Documentation/devicetree/bindings/leds/backlight
+F:	Documentation/ABI/stable/sysfs-class-backlight
+F:	Documentation/ABI/testing/sysfs-class-backlight
 
 BATMAN ADVANCED
 M:	Marek Lindner <mareklindner@neomailbox.ch>

drivers/video/backlight/Kconfig

@@ -10,7 +10,6 @@ menu "Backlight & LCD device support"
 #
 config LCD_CLASS_DEVICE
         tristate "Lowlevel LCD controls"
-	default m
 	help
 	  This framework adds support for low-level control of LCD.
 	  Some framebuffer devices connect to platform-specific LCD modules
@@ -143,7 +142,6 @@ endif # LCD_CLASS_DEVICE
 #
 config BACKLIGHT_CLASS_DEVICE
         tristate "Lowlevel Backlight controls"
-	default m
 	help
 	  This framework adds support for low-level control of the LCD
           backlight. This includes support for brightness and power.

drivers/video/backlight/backlight.c

@@ -32,6 +32,12 @@ static const char *const backlight_types[] = {
 	[BACKLIGHT_FIRMWARE] = "firmware",
 };
 
+static const char *const backlight_scale_types[] = {
+	[BACKLIGHT_SCALE_UNKNOWN]	= "unknown",
+	[BACKLIGHT_SCALE_LINEAR]	= "linear",
+	[BACKLIGHT_SCALE_NON_LINEAR]	= "non-linear",
+};
+
 #if defined(CONFIG_FB) || (defined(CONFIG_FB_MODULE) && \
 			   defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
 /* This callback gets called when something important happens inside a
@@ -246,6 +252,18 @@ static ssize_t actual_brightness_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(actual_brightness);
 
+static ssize_t scale_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct backlight_device *bd = to_backlight_device(dev);
+
+	if (WARN_ON(bd->props.scale > BACKLIGHT_SCALE_NON_LINEAR))
+		return sprintf(buf, "unknown\n");
+
+	return sprintf(buf, "%s\n", backlight_scale_types[bd->props.scale]);
+}
+static DEVICE_ATTR_RO(scale);
+
 static struct class *backlight_class;
 
 #ifdef CONFIG_PM_SLEEP
@@ -292,6 +310,7 @@ static struct attribute *bl_device_attrs[] = {
 	&dev_attr_brightness.attr,
 	&dev_attr_actual_brightness.attr,
 	&dev_attr_max_brightness.attr,
+	&dev_attr_scale.attr,
 	&dev_attr_type.attr,
 	NULL,
 };

drivers/video/backlight/gpio_backlight.c

@@ -59,13 +59,11 @@ static int gpio_backlight_probe_dt(struct platform_device *pdev,
 				   struct gpio_backlight *gbl)
 {
 	struct device *dev = &pdev->dev;
-	enum gpiod_flags flags;
 	int ret;
 
 	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);
+	gbl->gpiod = devm_gpiod_get(dev, NULL, GPIOD_ASIS);
 	if (IS_ERR(gbl->gpiod)) {
 		ret = PTR_ERR(gbl->gpiod);
 
@@ -79,6 +77,22 @@ static int gpio_backlight_probe_dt(struct platform_device *pdev,
 	return 0;
 }
 
+static int gpio_backlight_initial_power_state(struct gpio_backlight *gbl)
+{
+	struct device_node *node = gbl->dev->of_node;
+
+	/* Not booted with device tree or no phandle link to the node */
+	if (!node || !node->phandle)
+		return gbl->def_value ? FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;
+
+	/* if the enable GPIO is disabled, do not enable the backlight */
+	if (gpiod_get_value_cansleep(gbl->gpiod) == 0)
+		return FB_BLANK_POWERDOWN;
+
+	return FB_BLANK_UNBLANK;
+}
+
+
 static int gpio_backlight_probe(struct platform_device *pdev)
 {
 	struct gpio_backlight_platform_data *pdata =
@@ -136,7 +150,9 @@ static int gpio_backlight_probe(struct platform_device *pdev)
 		return PTR_ERR(bl);
 	}
 
-	bl->props.brightness = gbl->def_value;
+	bl->props.power = gpio_backlight_initial_power_state(gbl);
+	bl->props.brightness = 1;
+
 	backlight_update_status(bl);
 
 	platform_set_drvdata(pdev, bl);

drivers/video/backlight/lm3630a_bl.c

@@ -377,8 +377,7 @@ static int lm3630a_parse_led_sources(struct fwnode_handle *node,
 	u32 sources[LM3630A_NUM_SINKS];
 	int ret, num_sources, i;
 
-	num_sources = fwnode_property_read_u32_array(node, "led-sources", NULL,
-						     0);
+	num_sources = fwnode_property_count_u32(node, "led-sources");
 	if (num_sources < 0)
 		return default_led_sources;
 	else if (num_sources > ARRAY_SIZE(sources))

drivers/video/backlight/lms283gf05.c

@@ -158,7 +158,7 @@ static int lms283gf05_probe(struct spi_device *spi)
 		ret = devm_gpio_request_one(&spi->dev, pdata->reset_gpio,
 				GPIOF_DIR_OUT | (!pdata->reset_inverted ?
 				GPIOF_INIT_HIGH : GPIOF_INIT_LOW),
-				"LMS285GF05 RESET");
+				"LMS283GF05 RESET");
 		if (ret)
 			return ret;
 	}

drivers/video/backlight/pwm_bl.c

@@ -387,6 +387,31 @@ int pwm_backlight_brightness_default(struct device *dev,
 }
 #endif
 
+static bool pwm_backlight_is_linear(struct platform_pwm_backlight_data *data)
+{
+	unsigned int nlevels = data->max_brightness + 1;
+	unsigned int min_val = data->levels[0];
+	unsigned int max_val = data->levels[nlevels - 1];
+	/*
+	 * Multiplying by 128 means that even in pathological cases such
+	 * as (max_val - min_val) == nlevels the error at max_val is less
+	 * than 1%.
+	 */
+	unsigned int slope = (128 * (max_val - min_val)) / nlevels;
+	unsigned int margin = (max_val - min_val) / 20; /* 5% */
+	int i;
+
+	for (i = 1; i < nlevels; i++) {
+		unsigned int linear_value = min_val + ((i * slope) / 128);
+		unsigned int delta = abs(linear_value - data->levels[i]);
+
+		if (delta > margin)
+			return false;
+	}
+
+	return true;
+}
+
 static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb)
 {
 	struct device_node *node = pb->dev->of_node;
@@ -536,6 +561,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 		goto err_alloc;
 	}
 
+	memset(&props, 0, sizeof(struct backlight_properties));
+
 	if (data->levels) {
 		/*
 		 * For the DT case, only when brightness levels is defined
@@ -548,6 +575,11 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 
 			pb->levels = data->levels;
 		}
+
+		if (pwm_backlight_is_linear(data))
+			props.scale = BACKLIGHT_SCALE_LINEAR;
+		else
+			props.scale = BACKLIGHT_SCALE_NON_LINEAR;
 	} else if (!data->max_brightness) {
 		/*
 		 * If no brightness levels are provided and max_brightness is
@@ -574,6 +606,8 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 
 			pb->levels = data->levels;
 		}
+
+		props.scale = BACKLIGHT_SCALE_NON_LINEAR;
 	} else {
 		/*
 		 * That only happens for the non-DT case, where platform data
@@ -584,7 +618,6 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 
 	pb->lth_brightness = data->lth_brightness * (state.period / pb->scale);
 
-	memset(&props, 0, sizeof(struct backlight_properties));
 	props.type = BACKLIGHT_RAW;
 	props.max_brightness = data->max_brightness;
 	bl = backlight_device_register(dev_name(&pdev->dev), &pdev->dev, pb,

drivers/video/backlight/rave-sp-backlight.c

@@ -48,14 +48,20 @@ static int rave_sp_backlight_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct backlight_device *bd;
 
-	bd = devm_backlight_device_register(dev, pdev->name, dev->parent,
+	bd = devm_backlight_device_register(dev, pdev->name, dev,
 					    dev_get_drvdata(dev->parent),
 					    &rave_sp_backlight_ops,
 					    &rave_sp_backlight_props);
 	if (IS_ERR(bd))
 		return PTR_ERR(bd);
 
-	backlight_update_status(bd);
+	/*
+	 * If there is a phandle pointing to the device node we can
+	 * assume that another device will manage the status changes.
+	 * If not we make sure the backlight is in a consistent state.
+	 */
+	if (!dev->of_node->phandle)
+		backlight_update_status(bd);
 
 	return 0;
 }

drivers/video/backlight/tosa_lcd.c

@@ -222,8 +222,7 @@ static int tosa_lcd_remove(struct spi_device *spi)
 {
 	struct tosa_lcd_data *data = spi_get_drvdata(spi);
 
-	if (data->i2c)
-		i2c_unregister_device(data->i2c);
+	i2c_unregister_device(data->i2c);
 
 	tosa_lcd_tg_off(data);
 

include/linux/backlight.h

@@ -46,6 +46,12 @@ enum backlight_notification {
 	BACKLIGHT_UNREGISTERED,
 };
 
+enum backlight_scale {
+	BACKLIGHT_SCALE_UNKNOWN = 0,
+	BACKLIGHT_SCALE_LINEAR,
+	BACKLIGHT_SCALE_NON_LINEAR,
+};
+
 struct backlight_device;
 struct fb_info;
 
@@ -80,6 +86,8 @@ struct backlight_properties {
 	enum backlight_type type;
 	/* Flags used to signal drivers of state changes */
 	unsigned int state;
+	/* Type of the brightness scale (linear, non-linear, ...) */
+	enum backlight_scale scale;
 
 #define BL_CORE_SUSPENDED	(1 << 0)	/* backlight is suspended */
 #define BL_CORE_FBBLANK		(1 << 1)	/* backlight is under an fb blank event */