[PATCH 2/2] ACPI / video / i915: Remove ACPI backlight if firmware expects Windows 8
jani.nikula at linux.intel.com
Wed Sep 11 01:45:19 PDT 2013
On Wed, 11 Sep 2013, Aaron Lu <aaron.lu at intel.com> wrote:
> It is possible the i915 driver decides not to register a backlight
> interface for the graphics card for some reason(memory allocation failed
> or it knows the native control does not work on this card or whatever),
> so I would prefer let i915 tell ACPI video that it has registered a
> native backlight control interface as Jani has said.
> Then together with the video.use_native_backlight, we can register or
> not register ACPI video backlight interface accordingly. Or rather, we
> can simply not register ACPI video backlight interface for Win8 systems
> as long as i915 indicates that it has native backlight control(if the
> native control is broken, i915 should fix it or blacklist it so that
> i915 will not indicate it has native backlight control and ACPI video
> will continue to register its own).
> How does this sound?
Sounds good to me.
Before plunging forward, have you observed any difference between the
boot modes? We have reports  that the backlight behaviour is
different with UEFI vs. UEFI+CSM or legacy boot. So I'm wondering if the
acpi_gbl_osi_data >= ACPI_OSI_WIN_8 check in patch 2/2 is the whole
Further, if we tell the BIOS we're Windows 8 to use the tested BIOS code
paths, what guarantees do we have of UEFI+CSM or legacy boots working?
Jani Nikula, Intel Open Source Technology Center
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