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

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Message-ID: <87hadrycf4.fsf@intel.com>
Date:	Wed, 11 Sep 2013 11:45:19 +0300
From:	Jani Nikula <jani.nikula@...ux.intel.com>
To:	Aaron Lu <aaron.lu@...el.com>, "Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Daniel Vetter <daniel@...ll.ch>, Aaron Lu <aaron.lu@...el.com>,
	ACPI Devel Mailing List <linux-acpi@...r.kernel.org>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	"intel-gfx\@lists.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	Yves-Alexis Perez <corsac@...ian.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel\@lists.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Seth Forshee <seth.forshee@...onical.com>,
	"Lee\, Chun-Yi" <joeyli.kernel@...il.com>,
	Igor Gnatenko <i.gnatenko.brain@...il.com>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Lee Chun-Yi <jlee@...ell.com>, Len Brown <lenb@...nel.org>
Subject: Re: [PATCH 2/2] ACPI / video / i915: Remove ACPI backlight if firmware expects Windows 8

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