iio: adc: ad7793: use read_avail iio hook for scale available

This change uses the read_avail and '.info_mask_shared_by_type_available'
modifier to set the available scale.
Essentially, nothing changes to the driver's ABI.

The main idea for this patch is to remove the AD7793 driver from
checkpatch's radar. There have been about ~3 attempts to fix/break the
'in_voltage-voltage_scale_available' attribute, because checkpatch assumed
it to be an arithmetic operation and people were trying to change that.
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7793.c

@@ -354,29 +354,28 @@ static IIO_CONST_ATTR_SAMP_FREQ_AVAIL(
 static IIO_CONST_ATTR_NAMED(sampling_frequency_available_ad7797,
 	sampling_frequency_available, "123 62 50 33 17 16 12 10 8 6 4");
 
-static ssize_t ad7793_show_scale_available(struct device *dev,
-			struct device_attribute *attr, char *buf)
+static int ad7793_read_avail(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     const int **vals, int *type, int *length,
+			     long mask)
 {
-	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct ad7793_state *st = iio_priv(indio_dev);
-	int i, len = 0;
 
-	for (i = 0; i < ARRAY_SIZE(st->scale_avail); i++)
-		len += sprintf(buf + len, "%d.%09u ", st->scale_avail[i][0],
-			       st->scale_avail[i][1]);
-
-	len += sprintf(buf + len, "\n");
+	switch (mask) {
+	case IIO_CHAN_INFO_SCALE:
+		*vals = (int *)st->scale_avail;
+		*type = IIO_VAL_INT_PLUS_NANO;
+		/* Values are stored in a 2D matrix  */
+		*length = ARRAY_SIZE(st->scale_avail) * 2;
 
-	return len;
+		return IIO_AVAIL_LIST;
+	default:
+		return -EINVAL;
+	}
 }
 
-static IIO_DEVICE_ATTR_NAMED(in_m_in_scale_available,
-		in_voltage-voltage_scale_available, S_IRUGO,
-		ad7793_show_scale_available, NULL, 0);
-
 static struct attribute *ad7793_attributes[] = {
 	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
-	&iio_dev_attr_in_m_in_scale_available.dev_attr.attr,
 	NULL
 };
 
@@ -534,6 +533,7 @@ static const struct iio_info ad7793_info = {
 	.read_raw = &ad7793_read_raw,
 	.write_raw = &ad7793_write_raw,
 	.write_raw_get_fmt = &ad7793_write_raw_get_fmt,
+	.read_avail = ad7793_read_avail,
 	.attrs = &ad7793_attribute_group,
 	.validate_trigger = ad_sd_validate_trigger,
 };
@@ -547,7 +547,7 @@ static const struct iio_info ad7797_info = {
 };
 
 #define __AD7793_CHANNEL(_si, _channel1, _channel2, _address, _bits, \
-	_storagebits, _shift, _extend_name, _type, _mask_all) \
+	_storagebits, _shift, _extend_name, _type, _mask_type_av, _mask_all) \
 	{ \
 		.type = (_type), \
 		.differential = (_channel2 == -1 ? 0 : 1), \
@@ -559,6 +559,7 @@ static const struct iio_info ad7797_info = {
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
 			BIT(IIO_CHAN_INFO_OFFSET), \
 		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
+		.info_mask_shared_by_type_available = (_mask_type_av), \
 		.info_mask_shared_by_all = _mask_all, \
 		.scan_index = (_si), \
 		.scan_type = { \
@@ -574,23 +575,41 @@ static const struct iio_info ad7797_info = {
 	_storagebits, _shift) \
 	__AD7793_CHANNEL(_si, _channel1, _channel2, _address, _bits, \
 		_storagebits, _shift, NULL, IIO_VOLTAGE, \
+		BIT(IIO_CHAN_INFO_SCALE), \
 		BIT(IIO_CHAN_INFO_SAMP_FREQ))
 
 #define AD7793_SHORTED_CHANNEL(_si, _channel, _address, _bits, \
 	_storagebits, _shift) \
 	__AD7793_CHANNEL(_si, _channel, _channel, _address, _bits, \
 		_storagebits, _shift, "shorted", IIO_VOLTAGE, \
+		BIT(IIO_CHAN_INFO_SCALE), \
 		BIT(IIO_CHAN_INFO_SAMP_FREQ))
 
 #define AD7793_TEMP_CHANNEL(_si, _address, _bits, _storagebits, _shift) \
 	__AD7793_CHANNEL(_si, 0, -1, _address, _bits, \
 		_storagebits, _shift, NULL, IIO_TEMP, \
+		0, \
 		BIT(IIO_CHAN_INFO_SAMP_FREQ))
 
 #define AD7793_SUPPLY_CHANNEL(_si, _channel, _address, _bits, _storagebits, \
 	_shift) \
 	__AD7793_CHANNEL(_si, _channel, -1, _address, _bits, \
 		_storagebits, _shift, "supply", IIO_VOLTAGE, \
+		0, \
+		BIT(IIO_CHAN_INFO_SAMP_FREQ))
+
+#define AD7797_DIFF_CHANNEL(_si, _channel1, _channel2, _address, _bits, \
+	_storagebits, _shift) \
+	__AD7793_CHANNEL(_si, _channel1, _channel2, _address, _bits, \
+		_storagebits, _shift, NULL, IIO_VOLTAGE, \
+		0, \
+		BIT(IIO_CHAN_INFO_SAMP_FREQ))
+
+#define AD7797_SHORTED_CHANNEL(_si, _channel, _address, _bits, \
+	_storagebits, _shift) \
+	__AD7793_CHANNEL(_si, _channel, _channel, _address, _bits, \
+		_storagebits, _shift, "shorted", IIO_VOLTAGE, \
+		0, \
 		BIT(IIO_CHAN_INFO_SAMP_FREQ))
 
 #define DECLARE_AD7793_CHANNELS(_name, _b, _sb, _s) \
@@ -620,8 +639,8 @@ const struct iio_chan_spec _name##_channels[] = { \
 
 #define DECLARE_AD7797_CHANNELS(_name, _b, _sb) \
 const struct iio_chan_spec _name##_channels[] = { \
-	AD7793_DIFF_CHANNEL(0, 0, 0, AD7793_CH_AIN1P_AIN1M, (_b), (_sb), 0), \
-	AD7793_SHORTED_CHANNEL(1, 0, AD7793_CH_AIN1M_AIN1M, (_b), (_sb), 0), \
+	AD7797_DIFF_CHANNEL(0, 0, 0, AD7793_CH_AIN1P_AIN1M, (_b), (_sb), 0), \
+	AD7797_SHORTED_CHANNEL(1, 0, AD7793_CH_AIN1M_AIN1M, (_b), (_sb), 0), \
 	AD7793_TEMP_CHANNEL(2, AD7793_CH_TEMP, (_b), (_sb), 0), \
 	AD7793_SUPPLY_CHANNEL(3, 3, AD7793_CH_AVDD_MONITOR, (_b), (_sb), 0), \
 	IIO_CHAN_SOFT_TIMESTAMP(4), \