Hi Matthew,
I'm reading this commit
fbc9fe1 ACPI / video: Do not register backlight if win8 and native
interface exists
It does what you say above.
But, the variable use_native_backlight is false by default, and user
has to enable this by adding one kernel parameter
video.use_native_backlight=1
I don't see this do any difference with acpi_backlight=vendor as user
has to add the kernel command line explicitly to get rid of the broken
acpi_video0.
We always encourage OEM BIOS to follow the ACPI spec., if not, we'll
ask them to remove _BCL, _BCM, _BQC functions.
And Dell Inspiron 3138 is the first one that they refuse our request,
so I would like to fix it in the kernel.
I don't know if this kind of case will increase or not, but Windows
doesn't use ACPI is not from Win8, but Win7 or even earlier.
Taking into account that use_native_backlight is false by default,
that commit doesn't fix my issue, and I don't know when is the
suitable time to enable it by default in the future.
So, I think we probably need some quirks to disable acpi_video0 by the
mean while before use_native_backlight is default true.
Best regards,
AceLan Kao.
2013/12/3 Matthew Garrett <mjg59@xxxxxxxxxxxxx>:
> On Tue, Dec 03, 2013 at 03:31:45PM +0800, AceLan Kao wrote:
>> Hi Matthew,
>>
>> Sorry, I don't understand what you mean.
>>
>> Let me explain it again.
>> The BIOS engineer refuse to remove the ACPI functions(_BCM) in BIOS code,
>> so we'll have acpi_video0 interface be created under
>> /sys/class/backlight/ and that interface doesn't work.
>> This patch is equal to add this kernel command line "acpi_backlight=vendor"
>> So that, there will be no acpi_video0 be create, and we will use
>> intel_backlight interface instead.
>
> Right. This isn't a Dell-specific problem. Windows 8 doesn't use the
> ACPI backlight interface, so any system that calls _OSI("Windows 2012")
> should use the Intel interface instead. It needs to be fixed in general,
> not in the platform drivers.
>
> --
> Matthew Garrett | mjg59@xxxxxxxxxxxxx
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--
Chia-Lin Kao(AceLan)
http://blog.acelan.idv.tw/
E-Mail: acelan.kaoATcanonical.com (s/AT/@/)
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