Hi,
On 8/18/22 22:07, Daniel Dadap wrote:
>
> On 8/18/22 1:42 PM, Hans de Goede wrote:
>> 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.wyso...@intel.com>
>> Signed-off-by: Hans de Goede <hdego...@redhat.com>
>> ---
>> drivers/acpi/acpi_video.c | 50 ++++++++++++++++++++++++++++++++++++---
>> include/acpi/video.h | 2 ++
>> 2 files changed, 49 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
>> index 8545bf94866f..09dd86f86cf3 100644
>> --- 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);
>
>
> Would it make sense to make this parameter writable from userspace, e.g. so
> that it can be set by a udev rule rather than relying on a riskier kernel
> command line edit? Then again, that probably makes things more complicated,
> since you'd have to check the parameter again when the worker fires, and
> changing the parameter to a non-zero value from either zero or a different
> non-zero value would be too weird. And making a separate writable parameter
> to allow userspace to turn the worker into a noop despite it being enabled
> when the kernel was initially loaded seems wrong, too.
Right, you have pretty much described yourself why making this parameter
runtime configurable is not really feasible :)
Regards,
Hans
>
>
>> +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(®ister_count_mutex);
>> return ret;
>> @@ -2245,6 +2277,7 @@ 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;
>> 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 4705e339c252..0625806d3bbd 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(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)
>> {
>
