platform/chrome: Expose Chrome OS Lightbar to users

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>
Tested-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/platform/chrome/cros_ec_dev.c b/drivers/platform/chrome/cros_ec_dev.c
index 33f37ad36892..ce714317a59e 100644
--- a/drivers/platform/chrome/cros_ec_dev.c
+++ b/drivers/platform/chrome/cros_ec_dev.c
@@ -200,6 +200,7 @@ static int ec_device_probe(struct platform_device *pdev)
 
 	/* Initialize extra interfaces */
 	ec_dev_sysfs_init(ec);
+	ec_dev_lightbar_init(ec);
 
 	return 0;
 }
@@ -208,6 +209,7 @@ static int ec_device_remove(struct platform_device *pdev)
 {
 	struct cros_ec_device *ec = dev_get_drvdata(pdev->dev.parent);
 
+	ec_dev_lightbar_remove(ec);
 	ec_dev_sysfs_remove(ec);
 	device_destroy(cros_class, MKDEV(ec_major, 0));
 	cdev_del(&ec->cdev);