Re: [REGRESSION] [v2] ACPI / video: Default lcd_only to true on Win8 ready and newer machines

[James Hogan <jhogan@kernel.org>]

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On Mon, Apr 16, 2018 at 01:07:50PM +0200, Hans de Goede wrote:
> On 16-04-18 00:54, James Hogan wrote:
> > On Sun, Apr 15, 2018 at 02:04:26PM +0200, Hans de Goede wrote:
> > > When you say quirk do you mean you add something to
> > > the kernel commandline to work around this?
> > 
> > No, it was automatic, in the source. I don't know this code well enough
> > to know how they got it working.
> 
> Weird, if my only_lcd changes impact you then acpi_osi_is_win8()
> returns true for you

It rings a bell that this laptop claims win8 support.

> you should get the intel backlight interface
> by default, but maybe the i915 driver somehow detects that that
> is not appropriate on your device ... ?
> 
> Before I can start working on a quirk to fix this I've some
> questions:
> 
> 1) With recent kernels without the 965736ee654d commit, what is
>    the output of "ls /sys/class/backlight" ?

$ ls -l /sys/class/backlight
total 0
lrwxrwxrwx 1 root root 0 Apr 16 13:57 acpi_video0 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0

> 2) What is the output of "ls /sys/class/backlight" after
>    commit 965736ee654d ?

no devices show up there.

> 3) Can you start a kernel with commit 965736ee654d in there and
>    "video.only_lcd=0" on the kernel commandline and verify that
>    this fixes backlight control for you ?

Confirmed, acpi_video0 shows up and backlight control works as expected.

Cheers
James

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