linux-kernel - Backlight driver for MacBook Air 6,1 and 6,2

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <CAMeQTsZhBV=OtuktfS4Da5Sq+76J_oNsXd8AjeTJCqoPGxC3GA@mail.gmail.com>
Date:	Tue, 21 Jan 2014 03:15:15 +0100
From:	Patrik Jakobsson <patrik.r.jakobsson@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, mjg59@...f.ucam.org,
	Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Backlight driver for MacBook Air 6,1 and 6,2

Hi Andrew and CCs

I've put together (rather quickly) a driver for directly handling the backlight
driver chip (LM8550) on the 2013 MacBook Air. It is needed to work around a bug
(likely in firmware) that occurs after suspend/resume. See:

https://bugs.freedesktop.org/show_bug.cgi?id=67454

This seems to fall outside of what the i915 driver should handle and thus need a
separate driver. It's available at: https://github.com/patjak/mba6x_bl

The MacBook Air provides ACPI backlight methods but they also break after
suspend. I'm planning to mainline this and have a few questions.

1) I'm accessing the LP8550 on the SMBUS through ACPI methods. Should I access
the SMBUS directly instead or is this ok? I probably need to look at locking
around SMBUS accesses.

2) Is DMI the proper way of probing? Currently I'm just checking if the chip is
there and that it returns the proper contents in an identifier byte.

3) I assume the backlight type should be BACKLIGHT_PLATFORM (currently
BACKLIGHT_FIRMWARE) but do I also need to blacklist the ACPI backlight on these
devices? How do I get the proper precedence over other backlight devices?

Is there still time to get this into 3.14-rc1?

Thanks
Patrik
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/