iio: cros_ec: add 'id' sysfs entry

This new sysfs entry is used to interpret ring buffer information,
mainly by Android sensor HAL.
It expand to all sensors, the documentation about 'id' we can found
in Documentation/ABI/testing/sysfs-bus-iio-cros-ec.

Also fix typo in docs, I replace 'Septembre' by 'September'.
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Fabien Lahoudere <fabien.lahoudere@collabora.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio-cros-ec

@@ -18,11 +18,11 @@ Description:
 		values are 'base' and 'lid'.
 
 What:		/sys/bus/iio/devices/iio:deviceX/id
-Date:		Septembre 2017
+Date:		September 2017
 KernelVersion:	4.14
 Contact:	linux-iio@vger.kernel.org
 Description:
-		This attribute is exposed by the CrOS EC legacy accelerometer
-		driver and represents the sensor ID as exposed by the EC. This
-		ID is used by the Android sensor service hardware abstraction
-		layer (sensor HAL) through the Android container on ChromeOS.
+		This attribute is exposed by the CrOS EC sensors driver and
+		represents the sensor ID as exposed by the EC. This ID is used
+		by the Android sensor service hardware abstraction layer (sensor
+		HAL) through the Android container on ChromeOS.

drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c

@@ -125,6 +125,15 @@ static ssize_t cros_ec_sensors_calibrate(struct iio_dev *indio_dev,
 	return ret ? ret : len;
 }
 
+static ssize_t cros_ec_sensors_id(struct iio_dev *indio_dev,
+				  uintptr_t private,
+				  const struct iio_chan_spec *chan, char *buf)
+{
+	struct cros_ec_sensors_core_state *st = iio_priv(indio_dev);
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", st->param.info.sensor_num);
+}
+
 static ssize_t cros_ec_sensors_loc(struct iio_dev *indio_dev,
 		uintptr_t private, const struct iio_chan_spec *chan,
 		char *buf)
@@ -140,6 +149,11 @@ const struct iio_chan_spec_ext_info cros_ec_sensors_ext_info[] = {
 		.shared = IIO_SHARED_BY_ALL,
 		.write = cros_ec_sensors_calibrate
 	},
+	{
+		.name = "id",
+		.shared = IIO_SHARED_BY_ALL,
+		.read = cros_ec_sensors_id
+	},
 	{
 		.name = "location",
 		.shared = IIO_SHARED_BY_ALL,