linux-kernel - Re: [PATCH] Implement direct pineview backlight control.

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Date:	Fri, 2 Jul 2010 16:12:30 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Bryan Freed <bfreed@...omium.org>
Cc:	airlied@...ux.ie, airlied@...hat.com, ben@...adent.org.uk,
	eric@...olt.net, mateusz.kaduk@...il.com, chris@...is-wilson.co.uk,
	bgamari.foss@...il.com, apw@...onical.com, yakui.zhao@...el.com,
	zhenyuw@...ux.intel.com, dri-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, Matthew Garrett <mjg@...hat.com>
Subject: Re: [PATCH] Implement direct pineview backlight control.

On Tue, 22 Jun 2010 16:58:27 -0700
Bryan Freed <bfreed@...omium.org> wrote:

> drm/i915: Add a direct interface for pineview backlight support.
> 
> This adds a Kconfig variable CONFIG_DRM_I915_DIRECT_BACKLIGHT to
> optionally include the new source file i915_backlight.c.  This file
> registers a couple backlight set/get routines with the standard
> drivers/video/backlight interface to add a directory under
> /sys/class/backlight/.
> 
> The big problem I see with this modification is that the i915 driver
> _already_ supports backlight level adjustment in i915_opregion.c.
> Unfortunately, that requires an IRQ to occur as the result of writing
> some ASLE (ACPI Source Language Event) register, and this requires
> BIOS support for the ACPI hook.  It looks like we will not have such
> support in our initial custom BIOS.
> 
> So I copy a small amount of code from i915_opregion.c to make backlight
> adjustment directly available to the backlight framework.
> 
> Another problem is that I do not cover all the cases handled by the
> i915_opregion.c code.  It would be too much untested code copying to
> do so.  I enforce the lack of support by checking for IS_PINEVIEW()
> in i915_backlight_init().
> 
> Review URL: http://codereview.chromium.org/2830015
> Signed-off-by: Bryan Freed <bfreed@...omium.org>

How does this compare to Matthew's native backlight support?  AFAIK
that patch is still outstanding due to the need for some changes to the
backlight subsystem.

Matthew?

-- 
Jesse Barnes, Intel Open Source Technology Center
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