Re: [PATCH] acpi: video: no automatic brightness changes by firmware

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

On 06/18/2013 08:13 AM, Aaron Lu wrote:
> On 06/18/2013 06:40 AM, Matthew Garrett wrote:
>> On Mon, Jun 17, 2013 at 09:01:10AM +0800, Aaron Lu wrote:
>>> Starting from win8, MS backlight control driver will set bit 2 of the
>>> parameter of control method _DOS, to inform firmware it should not
>>> perform any automatic brightness changes. This mostly affects hotkey
>>> notification deliver - if we do not set this bit, on hotkey press,
>>> firmware may choose to adjust brightness level instead of sending out
>>> notification and doing nothing.
>>
>> It's worth noting that this is a change in behaviour, and there's at 
>> least one VIA-based netbook where making this change breaks backlight 
>> control.
> 
> Thanks for pointing this out.
> Do you have any more information about this system, like its ACPI dump?
> 
> BTW, perhaps we should make this behavior change only for win8 systems?

Just checked all affected systems:
https://bugzilla.kernel.org/show_bug.cgi?id=51051
https://bugzilla.kernel.org/show_bug.cgi?id=56711
https://bugzilla.kernel.org/show_bug.cgi?id=52951

All systems claim win8 in _OSI, so I suppose I'll make this behavior
change only for those systems with the help of the recently proposed
"Expose OSI version" patchset.

Please let me know if you disagree, thanks.

-Aaron