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leds: add output inversion option to backlight trigger 

Extend the LED backlight tirgger driver with an option that allows for
inverting the trigger output polarity.

With the invertion option provided, I (ab)use the backlight trigger for
driving a LED that indicates LCD display blank condtition on my Amstrad
Delta videophone.  Since the machine has no dedicated power LED, it was
not possible to distinguish if the display was blanked, or the machine was
turned off, without touching it.

The invert sysfs control is patterned after a similiar function of the GPIO
trigger driver.

[akpm@linux-foundation.org: make output match input, tighten input checking]
[akpm@linux-foundation.org: make output match input, tighten input checking]
Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Cc: Paul Mundt <lethal@linux-sh.org>
Acked-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Janusz Krzysztofik 2011-01-12 16:59:20 -08:00 committed by Linus Torvalds
parent 61a83932b8
commit 9f9455ae71
2 changed files with 66 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
Documentation/ABI/testing/sysfs-class-led
View File

@ -26,3 +26,12 @@ Description:
scheduler is chosen. Trigger specific parameters can appear in
/sys/class/leds/<led> once a given trigger is selected.
What: /sys/class/leds/<led>/inverted
Date: January 2011
KernelVersion: 2.6.38
Contact: Richard Purdie <rpurdie@rpsys.net>
Description:
Invert the LED on/off state. This parameter is specific to
gpio and backlight triggers. In case of the backlight trigger,
it is usefull when driving a LED which is intended to indicate
a device in a standby like state.

61
drivers/leds/ledtrig-backlight.c
View File

@ -26,6 +26,7 @@ struct bl_trig_notifier {
int brightness;
int old_status;
struct notifier_block notifier;
unsigned invert;
};
static int fb_notifier_callback(struct notifier_block *p,
@ -36,23 +37,64 @@ static int fb_notifier_callback(struct notifier_block *p,
struct led_classdev *led = n->led;
struct fb_event *fb_event = data;
int *blank = fb_event->data;
int new_status = *blank ? BLANK : UNBLANK;
switch (event) {
case FB_EVENT_BLANK :
if (*blank && n->old_status == UNBLANK) {
if (new_status == n->old_status)
break;
if ((n->old_status == UNBLANK) ^ n->invert) {
n->brightness = led->brightness;
led_set_brightness(led, LED_OFF);
n->old_status = BLANK;
} else if (!*blank && n->old_status == BLANK) {
} else {
led_set_brightness(led, n->brightness);
n->old_status = UNBLANK;
}
n->old_status = new_status;
break;
}
return 0;
}
static ssize_t bl_trig_invert_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct led_classdev *led = dev_get_drvdata(dev);
struct bl_trig_notifier *n = led->trigger_data;
return sprintf(buf, "%u\n", n->invert);
}
static ssize_t bl_trig_invert_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t num)
{
struct led_classdev *led = dev_get_drvdata(dev);
struct bl_trig_notifier *n = led->trigger_data;
unsigned long invert;
int ret;
ret = strict_strtoul(buf, 10, &invert);
if (ret < 0)
return ret;
if (invert > 1)
return -EINVAL;
n->invert = invert;
/* After inverting, we need to update the LED. */
if ((n->old_status == BLANK) ^ n->invert)
led_set_brightness(led, LED_OFF);
else
led_set_brightness(led, n->brightness);
return num;
}
static DEVICE_ATTR(inverted, 0644, bl_trig_invert_show, bl_trig_invert_store);
static void bl_trig_activate(struct led_classdev *led)
{
int ret;
@ -66,6 +108,10 @@ static void bl_trig_activate(struct led_classdev *led)
return;
}
ret = device_create_file(led->dev, &dev_attr_inverted);
if (ret)
goto err_invert;
n->led = led;
n->brightness = led->brightness;
n->old_status = UNBLANK;
@ -74,6 +120,12 @@ static void bl_trig_activate(struct led_classdev *led)
ret = fb_register_client(&n->notifier);
if (ret)
dev_err(led->dev, "unable to register backlight trigger\n");
return;
err_invert:
led->trigger_data = NULL;
kfree(n);
}
static void bl_trig_deactivate(struct led_classdev *led)
@ -82,6 +134,7 @@ static void bl_trig_deactivate(struct led_classdev *led)
(struct bl_trig_notifier *) led->trigger_data;
if (n) {
device_remove_file(led->dev, &dev_attr_inverted);
fb_unregister_client(&n->notifier);
kfree(n);
}