iio: cros_ec_accel_legacy: Add Read Only frequency entries

Report to user space that 10Hz is the sampling frequency of
the accelerometers in legacy mode, and it can not be changed.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/accel/cros_ec_accel_legacy.c

@@ -33,6 +33,11 @@
  */
 #define ACCEL_LEGACY_NSCALE 9586168
 
+/*
+ * Sensor frequency is hard-coded to 10Hz.
+ */
+static const int cros_ec_legacy_sample_freq[] = { 10, 0 };
+
 static int cros_ec_accel_legacy_read_cmd(struct iio_dev *indio_dev,
 				  unsigned long scan_mask, s16 *data)
 {
@@ -96,6 +101,11 @@ static int cros_ec_accel_legacy_read(struct iio_dev *indio_dev,
 		*val = 0;
 		ret = IIO_VAL_INT;
 		break;
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*val = cros_ec_legacy_sample_freq[0];
+		*val2 = cros_ec_legacy_sample_freq[1];
+		ret = IIO_VAL_INT_PLUS_MICRO;
+		break;
 	default:
 		ret = cros_ec_sensors_core_read(st, chan, val, val2,
 				mask);
@@ -120,9 +130,39 @@ static int cros_ec_accel_legacy_write(struct iio_dev *indio_dev,
 	return -EINVAL;
 }
 
+/**
+ * cros_ec_accel_legacy_read_avail() - get available values
+ * @indio_dev:		pointer to state information for device
+ * @chan:	channel specification structure table
+ * @vals:	list of available values
+ * @type:	type of data returned
+ * @length:	number of data returned in the array
+ * @mask:	specifies which values to be requested
+ *
+ * Return:	an error code or IIO_AVAIL_LIST
+ */
+static int cros_ec_accel_legacy_read_avail(struct iio_dev *indio_dev,
+					   struct iio_chan_spec const *chan,
+					   const int **vals,
+					   int *type,
+					   int *length,
+					   long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_SAMP_FREQ:
+		*length = ARRAY_SIZE(cros_ec_legacy_sample_freq);
+		*vals = cros_ec_legacy_sample_freq;
+		*type = IIO_VAL_INT_PLUS_MICRO;
+		return IIO_AVAIL_LIST;
+	}
+
+	return -EINVAL;
+}
+
 static const struct iio_info cros_ec_accel_legacy_info = {
 	.read_raw = &cros_ec_accel_legacy_read,
 	.write_raw = &cros_ec_accel_legacy_write,
+	.read_avail = &cros_ec_accel_legacy_read_avail,
 };
 
 /*
@@ -142,7 +182,11 @@ static const struct iio_info cros_ec_accel_legacy_info = {
 		.info_mask_separate =					\
 			BIT(IIO_CHAN_INFO_RAW) |			\
 			BIT(IIO_CHAN_INFO_CALIBBIAS),			\
-		.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SCALE),	\
+		.info_mask_shared_by_all =				\
+			BIT(IIO_CHAN_INFO_SCALE) |			\
+			BIT(IIO_CHAN_INFO_SAMP_FREQ),			\
+		.info_mask_shared_by_all_available =			\
+			BIT(IIO_CHAN_INFO_SAMP_FREQ),			\
 		.ext_info = cros_ec_sensors_ext_info,			\
 		.scan_type = {						\
 			.sign = 's',					\