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) +void backlight_notify_brightness(struct backlight_device *bd); +#else +static inline void backlight_notify_brightness(struct backlight_device *bd) {} +#endif + /** * backlight_update_status - force an update of the backlight device status * @bd: the backlight device @@ -325,6 +351,10 @@ static inline int backlight_update_status(struct backlight_device *bd) ret = bd->ops->update_status(bd); mutex_unlock(&bd->update_lock); + /* Notify DRM and other listeners that brightness changed */ + if (ret == 0) + backlight_notify_brightness(bd); + return ret; } @@ -431,6 +461,21 @@ static inline void backlight_notify_blank_all(struct device *display_dev, { } #endif +int backlight_set_brightness(struct backlight_device *bd, unsigned int value, + enum backlight_update_reason reason); + +static inline void backlight_device_ref(struct backlight_device *bd) +{ + if (bd) + get_device(&bd->dev); +} + +static inline void backlight_device_unref(struct backlight_device *bd) +{ + if (bd) + put_device(&bd->dev); +} + #define to_backlight_device(obj) container_of(obj, struct backlight_device, dev) /** -- 2.43.0
