Hi Hans, Hans de Goede <hdegoede@xxxxxxxxxx> 於 2023年6月13日 週二 下午4:54寫道： > > Hi AceLan, > > On 6/13/23 09:30, AceLan Kao wrote: > > Hans de Goede <hdegoede@xxxxxxxxxx> 於 2023年6月8日 週四 下午5:16寫道： > >> > >> 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 > >> > > > > Hi Hans, > > > > I got another issue on the same platform. > > The first issue was that when set to DSC graphics only in the BIOS, > > I encountered the issue I reported here, dell_laptop creates dell_backlight > > and then nvidia creates nvidia_0 later. > > > > Now, set to hybrid mode in the BIOS, I found I still got 2 backlight interfaces > > $ ls /sys/class/backlight/ > > acpi_video0 intel_backlight > > acpi_video0 is redundant and non-working. > > > > Do you think should I set this platform to the dmi quirk? Or is there anything > > I could try to get rid of this? > > > This is very hard to answer without more info. > > For starters please make sure that you are testing with the latest kernel and > provide full dmesg output for a boot with the BIOS set to hybrid mode. > > Regards, > > Hans > Sorry to bother you, the issue has been fixed by the below commit. e506731c8f35 ("ACPI: video: Make acpi_backlight=video work independent from GPU driver") Thanks.
