[PATCH v5 0/4] Fix Win8 backlight issue

[Josh Boyer]

On Fri, Oct 11, 2013 at 6:10 PM, Rafael J. Wysocki <rjw at rjwysocki.net> wrote:
> On Friday, October 11, 2013 12:42:43 PM Josh Boyer wrote:
>> On Fri, Oct 11, 2013 at 9:27 AM, Aaron Lu <aaron.lu at intel.com> wrote:
>> > v5:
>> > 1 Introduce video.use_native_backlight module parameter and set its
>> >   value to false by default as suggested by Rafael. For Win8 systems
>> >   which have broken ACPI video backlight control, the parameter can be
>> >   set to 1 in kernel cmdline to skip registering ACPI video's backlight
>> >   interface. Due to this change, the acpi_video_verify_backlight_support
>> >   is moved from video_detect.c to video.c - patch 3/4;
>>
>> That's a fairly untenable position for distro kernels to be in.  They
>> now have to ask every user that reports an issue with the backlight to
>> try setting that option on the command line.  While I appreciate the
>> setting breaks things for some people, doesn't the Win8 issue impact
>> far more people?  Shouldn't it be defaulted to true?
>
> Well, we have a rule in the kernel not to introduce regressions for users even
> if they are minority.
>
>> If nothing else, can you add a config option for the default so
>> distros can use that to decide which way to default it and then work
>> on fixing the remaining users that have troubles?
>
> The current plan is to create a blacklist of systems where that option should
> be set.  We actually already have one, but it is at the _OSI() level, which
> is overkill in my view and may affect things beyond backlight.  Along with that
> we will debug systems where setting that option (to true) causes problems to
> happen, so that we'll be able to drop it going forward (hopefully).
>
> Of course, distro kernels may always change the default to true if they want.

They can, but they'd need to either patch the kernel to do so, or code
it in userspace bootloader configs.  Having a config option they can
set to change the default makes it reasonable and contained within the
kernel.

josh