Re: [PATCH] Documentation: Add entry for dell-laptop sysfs interface

From: Brian Norris
Date: Wed Dec 31 2014 - 00:32:14 EST


On Wed, Dec 03, 2014 at 06:41:33PM +0100, Gabriele Mazzotta wrote:
> Add the documentation for the new sysfs interface of dell-laptop
> that allows to configure the keyboard illumination on Dell systems.
> Signed-off-by: Gabriele Mazzotta <gabriele.mzt@xxxxxxxxx>
> Signed-off-by: Pali Rohár <pali.rohar@xxxxxxxxx>
> ---
> .../ABI/testing/sysfs-platform-dell-laptop | 60 ++++++++++++++++++++++
> 1 file changed, 60 insertions(+)
> create mode 100644 Documentation/ABI/testing/sysfs-platform-dell-laptop
> diff --git a/Documentation/ABI/testing/sysfs-platform-dell-laptop b/Documentation/ABI/testing/sysfs-platform-dell-laptop
> new file mode 100644
> index 0000000..7969443
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-platform-dell-laptop
> @@ -0,0 +1,60 @@
> +What: /sys/class/leds/dell::kbd_backlight/als_setting
> +Date: December 2014
> +KernelVersion: 3.19
> +Contact: Gabriele Mazzotta <gabriele.mzt@xxxxxxxxx>,
> + Pali Rohár <pali.rohar@xxxxxxxxx>
> +Description:
> + This file allows to control the automatic keyboard
> + illumination mode on some systems that have an ambient
> + light sensor. Write 1 to this file to enable the auto
> + mode, 0 to disable it.

This entry appears wrong, or at least incomplete. My system boots with a
default value of 18, and the 'set' implementation accepts any value from
0 to 255.

According to the comments in dell-laptop.c, the value actually means
something different than on/off:

cbArg3, byte0 Desired setting of ALS value that turns the light on or off.

Admittedly, I'm not clear on what the intended interface is, as I've
never had the ALS / keyboard backlight controls all working properly on
my laptop in the first place, but I thought this would be the right
place to ask about getting the documentation and driver in sync.

NB: I came across this because

(1) I'd really like to be able to turn the keyboard backlight on, the
timeout off, and the ALS off; and

(2) I noticed there was a new driver patch in 3.19 (nice! thanks!),
where previously there must have been some kind of half-functional
working driver -- I could get backlight control, but it always timed
out too quickly.

It seems like /sys/.../als_setting is documented to handle the latter
part of (1), but its implementation does not match.


P.S. The author of this page [1] might be interested in these new driver

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at