[PATCH 2/2] ACPI / video / i915: Remove ACPI backlight if firmware expects Windows 8
matthew.garrett at nebula.com
Wed Sep 11 03:30:17 PDT 2013
On Wed, 2013-09-11 at 13:29 +0300, Jani Nikula wrote:
> On Wed, 11 Sep 2013, Matthew Garrett <matthew.garrett at nebula.com> wrote:
> > On Wed, 2013-09-11 at 11:45 +0300, Jani Nikula wrote:
> >> 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
> >> story.
> >> 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?
> > We have no evidence of Windows behaving differently based on the exposed
> > firmware type.
> By "behaving differently", do you mean internally adapting to the boot
> mode, or exhibiting different behaviour to the user?
As far as backlight control goes, both.
> We have evidence of the firmware behaving differently (VBT, backlight)
> based on the boot mode, all else being equal. We don't adapt to that,
> and we fail. I don't know if we should adapt, or do things differently
> altogether. I don't even know if Windows 8 works on all boot modes on
> the machines in question.
Sure, but Windows knows nothing about VBT or opregion-backed backlight
control. That's up to the Intel driver.
Matthew Garrett <matthew.garrett at nebula.com>
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