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

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Date:	Tue, 30 Dec 2014 21:31:49 -0800
From:	Brian Norris <computersforpeace@...il.com>
To:	Gabriele Mazzotta <gabriele.mzt@...il.com>
Cc:	dvhart@...radead.org, mjg59@...f.ucam.org,
	linux-api@...r.kernel.org, platform-driver-x86@...r.kernel.org,
	linux-kernel@...r.kernel.org, libsmbios-devel@...ts.us.dell.com,
	Srinivas_G_Gowda@...l.com, Michael_E_Brown@...l.com,
	pali.rohar@...il.com, A.Sloman@...bham.ac.uk
Subject: Re: [PATCH] Documentation: Add entry for dell-laptop sysfs interface

Hi,

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@...il.com>
> Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> ---
>  .../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@...il.com>,
> +		Pali Rohár <pali.rohar@...il.com>
> +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.

Thanks,
Brian

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

[1] http://www.cs.bham.ac.uk/~axs/laptop/dell-e6410-fn-keys.html
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