Re: [PATCH v3] ACPI / video: Add systems that should favor native backlight interface

[Aaron Lu <aaron.lu@intel.com>]

On 01/21/2014 11:17 AM, Matthew Garrett wrote:
> On Tue, 2014-01-21 at 10:24 +0800, Aaron Lu wrote:
>> On 01/20/2014 09:34 PM, Matthew Garrett wrote:
>>> On Mon, 2014-01-20 at 16:12 +0800, Aaron Lu wrote:
>>>
>>>> 1 remove the win8 OSI check, I've seen win7 laptops that also needs to
>>>>   have only the GPU interface left and checking win8 doesn't make much
>>>>   sense now;
>>>
>>> Are we sure that those aren't simply some other bug?
>>
>> Well, the firmware on that laptop makes use of EC to do backlight
>> control and the fact that the firmware interface doesn't work while the
>> GPU's work seems to indicate that the backlight control circuit is not
>> routed to EC. I think this is the same case as Win8 laptops.
> 
> We know that Windows 8 graphics drivers don't use the ACPI interface,
> and that systems change their behaviour as a result, in some cases with
> absolutely no way for the ACPI interface could possibly work. I haven't
> seen any cases where that's obviously true for any non-Windows 8

Perhaps I'm not clear, I didn't mean non-Windows 8 systems will all favor
GPU's interface, I just meant for one specific win7 laptop I could re-use
the existing code to make the GPU's interface as the only one left. And to
achieve this, the Win8 OSI check in acpi_video_verify_backlight_support
has to be gone.

BTW, I actually think use_native_backlight param should mean "the native
backlight control interface will be the only one available on the system",
it doesn't need to go side by side with Win8 OSI check.

> systems. EC interfaces that don't work are often due to Linux leaving
> the hardware in a state other than the one expected by the firmware. We

Good to know this, thanks.

> shouldn't assume that it's the same issue until we've investigated
> further.

OK, but I honestly don't have any idea how to proceed, in case you have
some time, the bug is:
https://bugzilla.kernel.org/show_bug.cgi?id=66501