[PATCH 2/2] ACPI / video / i915: Remove ACPI backlight if firmware expects Windows 8

Jani Nikula jani.nikula at linux.intel.com
Wed Sep 11 03:29:29 PDT 2013

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 [1] 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?

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.


Jani Nikula, Intel Open Source Technology Center

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