ACPI: video: Make backlight class device registration a separate step (v2)

On x86/ACPI boards the acpi_video driver will usually initialize 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.

Changes in v2:
- Make register_backlight_delay a module parameter, mainly so that it can
  be disabled by Nvidia binary driver users

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 8545bf94866f09cd04ad44b3168fffed9ae685cf..09dd86f86cf330052d1a57537ee30bad7ca10c1b 100644 (file)
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -73,6 +73,16 @@ module_param(device_id_scheme, bool, 0444);
 static int only_lcd = -1;
 module_param(only_lcd, int, 0444);
 
+/*
+ * 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.
+ */
+static int register_backlight_delay = 8;
+module_param(register_backlight_delay, int, 0444);
+MODULE_PARM_DESC(register_backlight_delay,
+       "Delay in seconds before doing fallback (non GPU driver triggered) "
+       "backlight registration, set to 0 to disable.");
+
 static bool may_report_brightness_keys;
 static int register_count;
 static DEFINE_MUTEX(register_count_mutex);
@@ -81,6 +91,9 @@ 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);
 
 /*
@@ -1859,8 +1872,6 @@ 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() != acpi_backlight_video)
                return 0;
 
@@ -2086,7 +2097,11 @@ 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;
@@ -2125,6 +2140,11 @@ 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)
@@ -2235,6 +2255,18 @@ 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.
+        */
+       if (register_backlight_delay)
+               schedule_delayed_work(&video_bus_register_backlight_work,
+                                     register_backlight_delay * HZ);
+
 leave:
        mutex_unlock(&register_count_mutex);
        return ret;
@@ -2245,6 +2277,7 @@ void acpi_video_unregister(void)
 {
        mutex_lock(&register_count_mutex);
        if (register_count) {
+               cancel_delayed_work_sync(&video_bus_register_backlight_work);
                acpi_bus_unregister_driver(&acpi_video_bus);
                register_count = 0;
                may_report_brightness_keys = false;
@@ -2253,6 +2286,17 @@ 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 4705e339c252cc16ca334f2c202d3cce9730f97e..0625806d3bbd7ae8da0f75b5503d12702a4d19a7 100644 (file)
--- 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(void);
@@ -69,6 +70,7 @@ 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)
 {