From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jani Nikula <jani.nikula@linux.intel.com>
Subject: Re: [PATCH 2/2] ACPI / video / i915: Remove ACPI
	backlight if firmware expects Windows 8
Date: Wed, 11 Sep 2013 11:45:19 +0300
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To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Matthew Garrett <matthew.garrett@nebula.com>, Seth Forshee <seth.forshee@canonical.com>, Henrique de Moraes Holschuh <hmh@hmh.eng.br>, Aaron Lu <aaron.lu@intel.com>, Daniel Vetter <daniel.vetter@ffwll.ch>, "intel-gfx@lists.freedesktop.org" <intel-gfx@lists.freedesktop.org>, Yves-Alexis Perez <corsac@debian.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>, ACPI Devel Mailing List <linux-acpi@vger.kernel.org>, "Lee,
	Chun-Yi" <joeyli.kernel@gmail.com>, Igor Gnatenko <i.gnatenko.brain@gmail.com>, Lee Chun-Yi <jlee@novell.com>, Len Brown <lenb@kernel.org>
List-Id: linux-acpi@vger.kernel.org

On Wed, 11 Sep 2013, Aaron Lu <aaron.lu@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 [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?

BR,
Jani.


[1] https://bugzilla.kernel.org/show_bug.cgi?id=47941#c96


-- 
Jani Nikula, Intel Open Source Technology Center