linux-kernel - backlight module for nvidia cards -- control backlight even with offb

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Message-ID: <87r6gmy8kh.fsf@pobox.com>
Date:	Sat, 12 Jan 2008 23:37:18 +0100
From:	Andy Wingo <wingo@...ox.com>
To:	debian-powerpc <debian-powerpc@...ts.debian.org>,
	nouveau@...ts.freedesktop.org
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org
Subject: backlight module for nvidia cards -- control backlight even with offb

Hi all,

I have a 12" powerbook, one of the last G4's, and have long been
irritated that I couldn't use offb because it has no backlight control.
This is more irritating now that the nouveau project's X drivers are
starting to work for me on PPC, but are incompatible with the nvidiafb
frame buffer.

I decided to rip out the backlight code from the nvidia frame buffer
into a separate module that can be loaded even when using offb as the
frame buffer. I am attaching the source, but you may find a tarball with
a makefile here:

  http://wingolog.org/pub/nvbacklight-0.1.tar.bz2

I do not know what the correct solution is. Ideally offb would export a
backlight device. I tried getting open firmware to give me the needed
information, but the "reg" entry for the backlight seems short, given
that the mac-io@17 #address-cells == 1 and #size-cells == 1:

  $ hd /proc/device-tree/pci@...00000/mac-io@...backlight@...0/reg 
  00000000  00 00 f3 00                                       |....|
  00000004

For that reason I'm copying Ben Herrenschmidt to see if he knows
something about a proper solution. For now I'll just add nvbacklight to
my /etc/modules. Ideas about a "proper solution" are appreciated.

Regards,

Andy

View attachment "nvbacklight.c" of type "text/plain" (6197 bytes)