Re: [PATCH 3/3] mfd: cros_ec: Expose Chrome OS Lightbar to users

[Lee Jones <lee.jones@linaro.org>]

On Mon, 17 Nov 2014, Javier Martinez Canillas wrote:

> From: Bill Richardson <wfrichar@chromium.org>
> 
> This adds some sysfs entries to provide userspace control of the
> four-element LED "lightbar" on the Chromebook Pixel. This only instantiates
> the lightbar controls if the device actually exists.
> 
> To prevent DoS attacks, this interface is limited to 20 accesses/second,
> although that rate can be adjusted by a privileged user.
> 
> On Chromebooks without a lightbar, this should have no effect. On the
> Chromebook Pixel, you should be able to do things like this:
> 
>     $ cd /sys/devices/virtual/chromeos/cros_ec/lightbar
>     $ echo 0x80 > brightness
>     $ echo 255 > brightness
>     $
>     $ cat sequence
>     S0
>     $ echo konami > sequence
>     $ cat sequence
>     KONAMI
>     $
>     $ cat sequence
>     S0
> 
> And
> 
>     $ cd /sys/devices/virtual/chromeos/cros_ec/lightbar
>     $ echo stop > sequence
>     $ echo "4 255 255 255" > led_rgb
>     $ echo "0 255 0 0  1 0 255 0  2 0 0 255  3 255 255 0" > led_rgb
>     $ echo run  > sequence
> 
> Test the DoS prevention with this:
> 
>     $ cd /sys/devices/virtual/chromeos/cros_ec/lightbar
>     $ echo 500 > interval_msec
>     $ time (cat version version version version version version version)
> 
> Signed-off-by: Bill Richardson <wfrichar@chromium.org>
> Reviewed-by: Olof Johansson <olofj@chromium.org>
> Tested-by: Doug Anderson <dianders@chromium.org>
> Reviewed-by: Benson Leung <bleung@chromium.org>
> Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
> ---
>  drivers/mfd/Makefile           |   2 +-
>  drivers/mfd/cros_ec_dev.c      |   2 +
>  drivers/mfd/cros_ec_dev.h      |   3 +
>  drivers/mfd/cros_ec_lightbar.c | 347 +++++++++++++++++++++++++++++++++++++++++

By the sounds of the description, it doesn't seem as though this
driver lives in MFD.  I suggest another home, such as drivers/led.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
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