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Subject[PATCH] backlight: add support for disabling backlights via sysfs
Date
There have been several attempts recently to find ways to disable broken
backlight interfaces on laptops, such as [1]. These haven't always
worked as well as hoped and tend to be driver-specific, so we're seeing
attempts to add an expanding number of interfaces between drivers to try
to cope with the situation, such as [2] and [3]. We're also seeing
difficulties properly expressing the inter-module dependencies[4].
Rather than trying to address this situation in a piecemeal fashion, we
should find a solution that deal with disabling broken backlights more
generically. This patch does so by adding an "enabled" attribute to
sysfs for backlight devices. Writing 0 to this attribute disables the
backlight, blocking most attempts to change the state. Tools like udev
can set use this attribute to disable known broken backlight interfaces,
and tools like gnome-settings-daemon can query the attribute to avoid
using disabled backlights.

[1] https://lkml.org/lkml/2012/3/22/156
[2] https://lkml.org/lkml/2012/3/15/529
[3] https://lkml.org/lkml/2012/6/13/48
[4] https://lkml.org/lkml/2012/6/28/159

Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Corentin Chary <corentin.chary@gmail.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
I wanted to send this out for comments to see how people felt about this
idea. If it's well received I can follow up with patches to remove the
acpi_video_unregister() and apple_bl_unregister() calls currently being
used for this purpose.

Documentation/ABI/stable/sysfs-class-backlight | 10 +++++
drivers/video/backlight/backlight.c | 54 +++++++++++++++++++++---
include/linux/backlight.h | 1 +
3 files changed, 59 insertions(+), 6 deletions(-)
diff --git a/Documentation/ABI/stable/sysfs-class-backlight b/Documentation/ABI/stable/sysfs-class-backlight
index 70302f3..3b3c477 100644
--- a/Documentation/ABI/stable/sysfs-class-backlight
+++ b/Documentation/ABI/stable/sysfs-class-backlight
@@ -54,3 +54,13 @@ Description:
backlight state. Platform interfaces are mostly a
holdover from pre-standardisation of firmware
interfaces.
+
+What: /sys/class/backlight/<backlight>/enabled
+Date: May 2012
+KernelVersion: 3.6
+Contact: Seth Forshee <seth.forshee@canonical.com>
+Description:
+ Enable or disable this <backlight>. Also shows whether
+ the backlight is enabled. This can be used by tools like
+ udev to disable backlights that are known to be broken
+ on a given platform.
diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 297db2f..5275738 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -53,7 +53,8 @@ static int fb_notifier_callback(struct notifier_block *self,
bd->props.state &= ~BL_CORE_FBBLANK;
else
bd->props.state |= BL_CORE_FBBLANK;
- backlight_update_status(bd);
+ if (!(bd->props.state & BL_CORE_DISABLED))
+ backlight_update_status(bd);
}
mutex_unlock(&bd->ops_lock);
return 0;
@@ -124,7 +125,7 @@ static ssize_t backlight_store_power(struct device *dev,

rc = -ENXIO;
mutex_lock(&bd->ops_lock);
- if (bd->ops) {
+ if (!(bd->props.state & BL_CORE_DISABLED) && bd->ops) {
pr_debug("set power to %lu\n", power);
if (bd->props.power != power) {
bd->props.power = power;
@@ -159,7 +160,7 @@ static ssize_t backlight_store_brightness(struct device *dev,
rc = -ENXIO;

mutex_lock(&bd->ops_lock);
- if (bd->ops) {
+ if (!(bd->props.state & BL_CORE_DISABLED) && bd->ops) {
if (brightness > bd->props.max_brightness)
rc = -EINVAL;
else {
@@ -206,6 +207,43 @@ static ssize_t backlight_show_actual_brightness(struct device *dev,
return rc;
}

+static ssize_t backlight_show_enabled(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct backlight_device *bd = to_backlight_device(dev);
+
+ return sprintf(buf, "%d\n", !(bd->props.state & BL_CORE_DISABLED));
+}
+
+static ssize_t backlight_store_enabled(struct device *dev,
+ struct device_attribute *attr, const char *buf, size_t count)
+{
+ struct backlight_device *bd = to_backlight_device(dev);
+ int rc;
+ unsigned long enabled;
+
+ rc = kstrtoul(buf, 0, &enabled);
+ if (rc)
+ return rc;
+ if (enabled != 0 && enabled != 1)
+ return -EINVAL;
+
+ mutex_lock(&bd->ops_lock);
+
+ if (enabled)
+ bd->props.state &= ~BL_CORE_DISABLED;
+ else
+ bd->props.state |= BL_CORE_DISABLED;
+
+ if (bd->ops)
+ backlight_update_status(bd);
+
+ mutex_unlock(&bd->ops_lock);
+
+ sysfs_notify(&bd->dev.kobj, NULL, "enabled");
+ return count;
+}
+
static struct class *backlight_class;

static int backlight_suspend(struct device *dev, pm_message_t state)
@@ -213,7 +251,8 @@ static int backlight_suspend(struct device *dev, pm_message_t state)
struct backlight_device *bd = to_backlight_device(dev);

mutex_lock(&bd->ops_lock);
- if (bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
+ if (!(bd->props.state & BL_CORE_DISABLED) &&
+ bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
bd->props.state |= BL_CORE_SUSPENDED;
backlight_update_status(bd);
}
@@ -227,7 +266,8 @@ static int backlight_resume(struct device *dev)
struct backlight_device *bd = to_backlight_device(dev);

mutex_lock(&bd->ops_lock);
- if (bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
+ if (!(bd->props.state & BL_CORE_DISABLED) &&
+ bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
bd->props.state &= ~BL_CORE_SUSPENDED;
backlight_update_status(bd);
}
@@ -250,6 +290,7 @@ static struct device_attribute bl_device_attributes[] = {
NULL),
__ATTR(max_brightness, 0444, backlight_show_max_brightness, NULL),
__ATTR(type, 0444, backlight_show_type, NULL),
+ __ATTR(enabled, 0644, backlight_show_enabled, backlight_store_enabled),
__ATTR_NULL,
};

@@ -265,7 +306,8 @@ void backlight_force_update(struct backlight_device *bd,
enum backlight_update_reason reason)
{
mutex_lock(&bd->ops_lock);
- if (bd->ops && bd->ops->get_brightness)
+ if (!(bd->props.state & BL_CORE_DISABLED) &&
+ bd->ops && bd->ops->get_brightness)
bd->props.brightness = bd->ops->get_brightness(bd);
mutex_unlock(&bd->ops_lock);
backlight_generate_event(bd, reason);
diff --git a/include/linux/backlight.h b/include/linux/backlight.h
index 5ffc6dd..31917d0 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -77,6 +77,7 @@ struct backlight_properties {

#define BL_CORE_SUSPENDED (1 << 0) /* backlight is suspended */
#define BL_CORE_FBBLANK (1 << 1) /* backlight is under an fb blank event */
+#define BL_CORE_DISABLED (1 << 2) /* backlight disabled by userspace */
#define BL_CORE_DRIVER4 (1 << 28) /* reserved for driver specific use */
#define BL_CORE_DRIVER3 (1 << 29) /* reserved for driver specific use */
#define BL_CORE_DRIVER2 (1 << 30) /* reserved for driver specific use */
--
1.7.9.5


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