linux-kernel - Re: 2.6.30-rc1 (latest git): thinkpad-acpi: cannot control brightness with hotkeys (BISECTED)

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Message-ID: <20090415200125.GA31483@srcf.ucam.org>
Date:	Wed, 15 Apr 2009 21:01:25 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Niel Lambrechts <niel.lambrechts@...il.com>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	yakui_zhao <yakui.zhao@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux.kernel" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: 2.6.30-rc1 (latest git): thinkpad-acpi: cannot control brightness with hotkeys (BISECTED)

On Wed, Apr 15, 2009 at 09:55:55PM +0200, Niel Lambrechts wrote:

> The behaviour seems slightly different from before your 74a365b3f354
> commit in that /sys/class/backlight remains empty until i915 gets loaded
> for the first time, the contents then persist even if i915 is unloaded.
> Perhaps the directory was populated by a different kernel module, since
> when I did the bisect yesterday the directory would be there on boot
> before I started X or loaded i915.

In the past the directory would be created when the acpi video driver 
was loaded, but probably wouldn't work. Doing it that way is a violation 
of the opregion spec and causes some machines to break in a horrible 
manner, so I'd prefer not to go back to that version...

>  I'm not sure if that matters to any other user-space app. (or if
> ideally one is supposed to be able to control brightness in the console
> without having to load i915), but it's fine for controlling brightness
> in Xorg.

If you use modesetting then you shouldn't need to launch X to get 
working brightness control. The problem with the old-style world is that 
you won't get interrupts until X comes up.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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