Hi AceLan, On 6/8/23 05:04, AceLan Kao wrote: > Hans de Goede <hdegoede@xxxxxxxxxx> 於 2023年6月8日 週四 上午3:16寫道： >> >> Hi, >> >> On 6/7/23 09:47, Matthew Garrett wrote: >>> On Wed, Jun 07, 2023 at 03:39:33PM +0800, AceLan Kao wrote: >>> >>>> What do you think if we unregister backlight devices if the backlight type >>>> is larger than the current registered one. >>>> Do this check in backlight_device_register() and unregister backlight >>>> devices by the order raw(1) > platform(2) > firmware(3) >>>> And maybe introduce a sticky bit into the backlight device if the backlight >>>> driver doesn't want to be removed. >>> >>> Hans looked at doing this, but there were some awkward corner cases. >>> When we first introduced this functionality, firmware was preferred to >>> platform was preferred to raw - but on Intel, at least, this behaviour >>> changed with later versions of Windows. I don't think there's a single >>> static policy that works, I think you need to pay attention to the hints >>> the platform gives you. How does Windows know which interface to use on >>> this platform? The simplest solution may actually just be for >>> dell-laptop to refuse to register a backlight if the platform claims to >>> be Windows 8 or later. >> >> I like that idea. >> >> AceLan, I guess that you hit this easy while testing on a (development) >> Meteor Lake platform ? >> >> I have had other/similar reports about Meteor Lake platforms. >> >> On hw from the last 10 years dell-laptop will not register >> its vendor-type backlight class device because >> acpi_video_get_backlight_type() will return acpi_backlight_video >> there (1) so it does not matter if the GPU driver shows up only >> later (2). >> >> But it seems that on Meteor Lake the ACPI tables will no longer >> contain acpi_video backlight control support which causes >> acpi_video_get_backlight_type() to return acpi_backlight_vendor (2). >> triggering the issue you are seeing. >> >> Can you give the attached patch a try please ? >> >> Regards, >> >> Hans >> >> >> 1) Starting with kernel >= 6.2 acpi_video.c will only register >> the /sys/class/backlight/acpi_video# node after a drm/kms drivers >> asks it to register it. >> >> 2) The native GPU driver will tell the drivers/acpi/video_detect.c >> code that native backlight control is available changing >> the return of acpi_video_get_backlight_type() to native, which >> is why loading the native GPU driver first also fixes this issue. > > Hi Hans, > > Yes, this patch works for me, thanks. > > BTW, I encountered this issue on the RPL platform. Thank you for testing. I have updated the commit message to reflect that this impacts both RPL and MTL platforms and submitted the fix upstream: https://lore.kernel.org/linux-acpi/20230608091258.7963-1-hdegoede@xxxxxxxxxx/ Regards, Hans
