On x86/ACPI boards the acpi_video driver will usually initializing before the kms driver (except i915). This causes /sys/class/backlight/acpi_video0 to show up and then the kms driver registers its own native backlight device after which the drivers/acpi/video_detect.c code unregisters the acpi_video0 device (when acpi_video_get_backlight_type()==native).
This means that userspace briefly sees 2 devices and the disappearing of acpi_video0 after a brief time confuses the systemd backlight level save/restore code, see e.g.: https://bbs.archlinux.org/viewtopic.php?id=269920
To fix this make backlight class device registration a separate step done by a new acpi_video_register_backlight() function. The intend is for this to be called by the drm/kms driver *after* it is done setting up its own native backlight device. So that acpi_video_get_backlight_type() knows if a native backlight will be available or not at acpi_video backlight registration time, avoiding the add + remove dance.
Note the new acpi_video_register_backlight() function is also called from a delayed work to ensure that the acpi_video backlight devices does get registered if necessary even if there is no drm/kms driver or when it is disabled.
Signed-off-by: Hans de Goede hdegoede@redhat.com --- drivers/acpi/acpi_video.c | 45 ++++++++++++++++++++++++++++++++++++--- include/acpi/video.h | 2 ++ 2 files changed, 44 insertions(+), 3 deletions(-)
diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c index 95d4868f6a8c..79e75dc86243 100644 --- a/drivers/acpi/acpi_video.c +++ b/drivers/acpi/acpi_video.c @@ -31,6 +31,12 @@ #define ACPI_VIDEO_BUS_NAME "Video Bus" #define ACPI_VIDEO_DEVICE_NAME "Video Device"
+/* + * Display probing is known to take up to 5 seconds, so delay the fallback + * backlight registration by 5 seconds + 3 seconds for some extra margin. + */ +#define ACPI_VIDEO_REGISTER_BACKLIGHT_DELAY (8 * HZ) + #define MAX_NAME_LEN 20
MODULE_AUTHOR("Bruno Ducrot"); @@ -80,6 +86,9 @@ static LIST_HEAD(video_bus_head); static int acpi_video_bus_add(struct acpi_device *device); static int acpi_video_bus_remove(struct acpi_device *device); static void acpi_video_bus_notify(struct acpi_device *device, u32 event); +static void acpi_video_bus_register_backlight_work(struct work_struct *ignored); +static DECLARE_DELAYED_WORK(video_bus_register_backlight_work, + acpi_video_bus_register_backlight_work); void acpi_video_detect_exit(void);
/* @@ -1862,8 +1871,6 @@ static int acpi_video_bus_register_backlight(struct acpi_video_bus *video) if (video->backlight_registered) return 0;
- acpi_video_run_bcl_for_osi(video); - if (acpi_video_get_backlight_type(false) != acpi_backlight_video) return 0;
@@ -2089,7 +2096,11 @@ static int acpi_video_bus_add(struct acpi_device *device) list_add_tail(&video->entry, &video_bus_head); mutex_unlock(&video_list_lock);
- acpi_video_bus_register_backlight(video); + /* + * The userspace visible backlight_device gets registered separately + * from acpi_video_register_backlight(). + */ + acpi_video_run_bcl_for_osi(video); acpi_video_bus_add_notify_handler(video);
return 0; @@ -2128,6 +2139,11 @@ static int acpi_video_bus_remove(struct acpi_device *device) return 0; }
+static void acpi_video_bus_register_backlight_work(struct work_struct *ignored) +{ + acpi_video_register_backlight(); +} + static int __init is_i740(struct pci_dev *dev) { if (dev->device == 0x00D1) @@ -2238,6 +2254,17 @@ int acpi_video_register(void) */ register_count = 1;
+ /* + * acpi_video_bus_add() skips registering the userspace visible + * backlight_device. The intend is for this to be registered by the + * drm/kms driver calling acpi_video_register_backlight() *after* it is + * done setting up its own native backlight device. The delayed work + * ensures that acpi_video_register_backlight() always gets called + * eventually, in case there is no drm/kms driver or it is disabled. + */ + schedule_delayed_work(&video_bus_register_backlight_work, + ACPI_VIDEO_REGISTER_BACKLIGHT_DELAY); + leave: mutex_unlock(®ister_count_mutex); return ret; @@ -2248,6 +2275,7 @@ void acpi_video_unregister(void) { mutex_lock(®ister_count_mutex); if (register_count) { + cancel_delayed_work_sync(&video_bus_register_backlight_work); acpi_bus_unregister_driver(&acpi_video_bus); register_count = 0; } @@ -2255,6 +2283,17 @@ void acpi_video_unregister(void) } EXPORT_SYMBOL(acpi_video_unregister);
+void acpi_video_register_backlight(void) +{ + struct acpi_video_bus *video; + + mutex_lock(&video_list_lock); + list_for_each_entry(video, &video_bus_head, entry) + acpi_video_bus_register_backlight(video); + mutex_unlock(&video_list_lock); +} +EXPORT_SYMBOL(acpi_video_register_backlight); + void acpi_video_unregister_backlight(void) { struct acpi_video_bus *video; diff --git a/include/acpi/video.h b/include/acpi/video.h index e31afb93379a..b2f7dc1f354a 100644 --- a/include/acpi/video.h +++ b/include/acpi/video.h @@ -53,6 +53,7 @@ enum acpi_backlight_type { #if IS_ENABLED(CONFIG_ACPI_VIDEO) extern int acpi_video_register(void); extern void acpi_video_unregister(void); +extern void acpi_video_register_backlight(void); extern int acpi_video_get_edid(struct acpi_device *device, int type, int device_id, void **edid); extern enum acpi_backlight_type acpi_video_get_backlight_type(bool native); @@ -68,6 +69,7 @@ extern int acpi_video_get_levels(struct acpi_device *device, #else static inline int acpi_video_register(void) { return -ENODEV; } static inline void acpi_video_unregister(void) { return; } +static inline void acpi_video_register_backlight(void) { return; } static inline int acpi_video_get_edid(struct acpi_device *device, int type, int device_id, void **edid) {