Re: [PATCH] platform/x86: dell-laptop: Add drm module soft dependency

[AceLan Kao]

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.