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Subject[PATCH] LEDs: allow led-drivers to use a wider than 0...255 range of brightness values
This patch allows drivers to override the default maximum brightness value of
255. We take care to preserve backwards-compatibility, so that user-space
ABI doesn't change for existing drivers. All existing drivers have been verified
to use a zero-initialised memory for their struct led_classdev objects, so that
they will get the default maximum value of 255. New user-space software
can use a new read-only sysfs file /sys/class/leds/*/max_brightness to
retrieve maximum supported brightness of a specific LED.

Signed-off-by: Guennadi Liakhovetski <lg@denx.de>
---
This will be needed for a new LED driver for an SPI DAC, used as a
photo-flash and for camera calibration, so, its brightness has to be
adjustable at a finer than 256 levels scale.

drivers/leds/led-class.c | 21 ++++++++++++++++++++-
drivers/leds/leds.h | 4 ++--
include/linux/leds.h | 1 +
3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 6c4a326..c3b4ace 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -64,7 +64,16 @@ static ssize_t led_brightness_store(struct device *dev,
return ret;
}

+static ssize_t led_max_brightness_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct led_classdev *led_cdev = dev_get_drvdata(dev);
+
+ return sprintf(buf, "%u\n", led_cdev->max_brightness);
+}
+
static DEVICE_ATTR(brightness, 0644, led_brightness_show, led_brightness_store);
+static DEVICE_ATTR(max_brightness, 0444, led_max_brightness_show, NULL);
#ifdef CONFIG_LEDS_TRIGGERS
static DEVICE_ATTR(trigger, 0644, led_trigger_show, led_trigger_store);
#endif
@@ -118,6 +127,13 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
list_add_tail(&led_cdev->node, &leds_list);
up_write(&leds_list_lock);

+ if (!led_cdev->max_brightness)
+ led_cdev->max_brightness = LED_FULL;
+
+ rc = device_create_file(led_cdev->dev, &dev_attr_max_brightness);
+ if (rc)
+ goto err_out_attr_max;
+
led_update_brightness(led_cdev);

#ifdef CONFIG_LEDS_TRIGGERS
@@ -135,9 +151,11 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)

#ifdef CONFIG_LEDS_TRIGGERS
err_out_led_list:
+ device_remove_file(led_cdev->dev, &dev_attr_max_brightness);
+#endif
+err_out_attr_max:
device_remove_file(led_cdev->dev, &dev_attr_brightness);
list_del(&led_cdev->node);
-#endif
err_out:
device_unregister(led_cdev->dev);
return rc;
@@ -152,6 +170,7 @@ EXPORT_SYMBOL_GPL(led_classdev_register);
*/
void led_classdev_unregister(struct led_classdev *led_cdev)
{
+ device_remove_file(led_cdev->dev, &dev_attr_max_brightness);
device_remove_file(led_cdev->dev, &dev_attr_brightness);
#ifdef CONFIG_LEDS_TRIGGERS
device_remove_file(led_cdev->dev, &dev_attr_trigger);
diff --git a/drivers/leds/leds.h b/drivers/leds/leds.h
index 5edbf52..2dd8ecb 100644
--- a/drivers/leds/leds.h
+++ b/drivers/leds/leds.h
@@ -20,8 +20,8 @@
static inline void led_set_brightness(struct led_classdev *led_cdev,
enum led_brightness value)
{
- if (value > LED_FULL)
- value = LED_FULL;
+ if (value > led_cdev->max_brightness)
+ value = led_cdev->max_brightness;
led_cdev->brightness = value;
if (!(led_cdev->flags & LED_SUSPENDED))
led_cdev->brightness_set(led_cdev, value);
diff --git a/include/linux/leds.h b/include/linux/leds.h
index d3a73f5..4f8b842 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -30,6 +30,7 @@ enum led_brightness {
struct led_classdev {
const char *name;
int brightness;
+ int max_brightness;
int flags;

#define LED_SUSPENDED (1 << 0)
--
1.5.4


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