So far backlights have only been controlled via sysfs. However, sysfs is
not a proper user-space API for runtime modifications, and never was
intended to provide such. The DRM drivers are now prepared to provide
such a backlight link so user-space can control backlight via DRM
connector properties. This allows us to employ the same access-management
we use for mode-setting.
This patch adds a few kernel-internal backlight helpers so we can modify
backlights from within DRM, a brightness-changed notification, and a
per-device takeover count so that legacy sysfs writes can be inhibited
(-EBUSY) while a luminance-aware DRM client is in control.
Signed-off-by: David Herrmann <[email protected]>
V2: Marta Lofstedt <[email protected]>
- rebase
- minor edit for checkpatch warning
Signed-off-by: Marta Lofstedt <[email protected]>
V3: Mario Limonciello (AMD) <[email protected]>
- rebase
- Use guard(mutex)
V4: Mario Limonciello (AMD) <[email protected]>
- Adjust return type for backlight_set_brightness() to return errors
- Stop clamping in backlight_set_brightness()
- Drop backlight_device_lookup()
Signed-off-by: Mario Limonciello (AMD) <[email protected]>
---
drivers/video/backlight/backlight.c | 66 +++++++++++++++++++++++++++++
include/linux/backlight.h | 45 ++++++++++++++++++++
2 files changed, 111 insertions(+)
diff --git a/drivers/video/backlight/backlight.c
b/drivers/video/backlight/backlight.c
index 4401f6294ccc8..1c700c1e77c3f 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -126,6 +126,9 @@ static void backlight_generate_event(struct
backlight_device *bd,
case BACKLIGHT_UPDATE_HOTKEY:
envp[0] = "SOURCE=hotkey";
break;
+ case BACKLIGHT_UPDATE_DRM:
+ envp[0] = "SOURCE=drm";
+ break;
default:
envp[0] = "SOURCE=unknown";
break;
@@ -150,6 +153,13 @@ static ssize_t bl_power_store(struct device *dev, struct
device_attribute *attr,
struct backlight_device *bd = to_backlight_device(dev);
unsigned long power, old_power;
+ /* A luminance-aware DRM client has taken over this backlight; the
+ * legacy sysfs interface is disabled until the last such client
+ * goes away.
+ */
+ if (atomic_read(&bd->drm_takeover) > 0)
+ return -EBUSY;
+
rc = kstrtoul(buf, 0, &power);
if (rc)
return rc;
@@ -214,6 +224,13 @@ static ssize_t brightness_store(struct device *dev,
struct backlight_device *bd = to_backlight_device(dev);
unsigned long brightness;
+ /* A luminance-aware DRM client has taken over this backlight; the
+ * legacy sysfs interface is disabled until the last such client
+ * goes away.
+ */
+ if (atomic_read(&bd->drm_takeover) > 0)
+ return -EBUSY;
+
rc = kstrtoul(buf, 0, &brightness);
if (rc)
return rc;
@@ -514,6 +531,41 @@ static int devm_backlight_device_match(struct device *dev,
void *res,
return *r == data;
}
+/**
+ * backlight_set_brightness - set brightness on a backlight device
+ * @bd: backlight device to operate on
+ * @value: brightness value to set on the device
+ * @reason: backlight-change reason to use for notifications
+ *
+ * This is the in-kernel API equivalent of writing into the 'brightness' sysfs
+ * file. It calls into the underlying backlight driver to change the brightness
+ * value.
+ * A uevent notification is sent with the reason set to @reason.
+ * Return: 0 if successfully notified, -EINVAL for invalid values, -ENXIO if
the
+ * device has no ops (e.g. it is being unregistered)
+ */
+int backlight_set_brightness(struct backlight_device *bd, unsigned int value,
+ enum backlight_update_reason reason)
+{
+ int rc = -ENXIO;
+
+ scoped_guard(mutex, &bd->ops_lock) {
+ if (bd->ops) {
+ if (value > bd->props.max_brightness)
+ return -EINVAL;
+
+ dev_dbg(&bd->dev, "set brightness to %u\n", value);
+ bd->props.brightness = value;
+ rc = backlight_update_status(bd);
+ }
+ }
+ if (rc == 0)
+ backlight_generate_event(bd, reason);
+
+ return rc;
+}
+EXPORT_SYMBOL_GPL(backlight_set_brightness);
+
/**
* backlight_register_notifier - get notified of backlight (un)registration
* @nb: notifier block with the notifier to call on backlight (un)registration
@@ -548,6 +600,20 @@ int backlight_unregister_notifier(struct notifier_block
*nb)
}
EXPORT_SYMBOL(backlight_unregister_notifier);
+/**
+ * backlight_notify_brightness - notify brightness change to listeners
+ * @bd: backlight device that changed
+ *
+ * Notify registered listeners that the backlight brightness has changed.
+ * This is called automatically after successful brightness updates.
+ */
+void backlight_notify_brightness(struct backlight_device *bd)
+{
+ blocking_notifier_call_chain(&backlight_notifier,
+ BACKLIGHT_BRIGHTNESS_CHANGED, bd);
+}
+EXPORT_SYMBOL(backlight_notify_brightness);
+
/**
* devm_backlight_device_register - register a new backlight device
* @dev: the device to register
diff --git a/include/linux/backlight.h b/include/linux/backlight.h
index 015183d129f96..fac1acbc698a1 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -31,6 +31,12 @@ enum backlight_update_reason {
* @BACKLIGHT_UPDATE_SYSFS: The backlight was updated using sysfs.
*/
BACKLIGHT_UPDATE_SYSFS,
+
+ /**
+ * @BACKLIGHT_UPDATE_DRM: The backlight was updated from DRM, i.e.
through
+ * a connector LUMINANCE property rather than the legacy sysfs
interface.
+ */
+ BACKLIGHT_UPDATE_DRM,
};
/**
@@ -82,6 +88,11 @@ enum backlight_notification {
* @BACKLIGHT_UNREGISTERED: The backlight revice is unregistered.
*/
BACKLIGHT_UNREGISTERED,
+
+ /**
+ * @BACKLIGHT_BRIGHTNESS_CHANGED: The backlight brightness has changed.
+ */
+ BACKLIGHT_BRIGHTNESS_CHANGED,
};
/** enum backlight_scale - the type of scale used for brightness values
@@ -310,8 +321,23 @@ struct backlight_device {
* @use_count: The number of unblanked displays.
*/
int use_count;
+
+ /**
+ * @drm_takeover: Number of luminance-aware DRM clients that have
+ * taken over brightness control of this device. When non-zero,
+ * writes to the legacy sysfs ``brightness`` attribute return
+ * ``-EBUSY``. Managed by the DRM backlight helpers.
+ */
+ atomic_t drm_takeover;
};
+/* Forward declaration for backlight_update_status */
+#if IS_REACHABLE(CONFIG_BACKLIGHT_CLASS_DEVICE)
