iio: add support for multiple scan types per channel

This adds new fields to the iio_channel structure to support multiple
scan types per channel. This is useful for devices that support multiple
resolution modes or other modes that require different data formats of
the raw data.

To make use of this, drivers need to implement the new callback
get_current_scan_type() to resolve the scan type for a given channel
based on the current state of the driver. There is a new scan_type_ext
field in the iio_channel structure that should be used to store the
scan types for any channel that has more than one. There is also a new
flag has_ext_scan_type that acts as a type discriminator for the
scan_type/ext_scan_type union. A union is used so that we don't grow
the size of the iio_channel structure and also makes it clear that
scan_type and ext_scan_type are mutually exclusive.

The buffer code is the only code in the IIO core code that is using the
scan_type field. This patch updates the buffer code to use the new
iio_channel_validate_scan_type() function to ensure it is returning the
correct scan type for the current state of the device when reading the
sysfs attributes. The buffer validation code is also update to validate
any additional scan types that are set in the scan_type_ext field. Part
of that code is refactored to a new function to avoid duplication.

Some userspace tools may need to be updated to re-read the scan type
after writing any other attribute. During testing, we noticed that we
had to restart iiod to get it to re-read the scan type after enabling
oversampling on the ad7380 driver.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240530-iio-add-support-for-multiple-scan-types-v3-3-cbc4acea2cfa@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

1 files changed, 80 insertions, 21 deletions

diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index 08103a9e77f7..0138b21b244f 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -365,9 +365,16 @@ static ssize_t iio_show_fixed_type(struct device *dev,
 				   struct device_attribute *attr,
 				   char *buf)
 {
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
-	const struct iio_scan_type *scan_type = &this_attr->c->scan_type;
-	u8 type = scan_type->endianness;
+	const struct iio_scan_type *scan_type;
+	u8 type;
+
+	scan_type = iio_get_current_scan_type(indio_dev, this_attr->c);
+	if (IS_ERR(scan_type))
+		return PTR_ERR(scan_type);
+
+	type = scan_type->endianness;
 
 	if (type == IIO_CPU) {
 #ifdef __LITTLE_ENDIAN
@@ -691,15 +698,18 @@ static ssize_t enable_show(struct device *dev, struct device_attribute *attr,
 	return sysfs_emit(buf, "%d\n", iio_buffer_is_active(buffer));
 }
 
-static unsigned int iio_storage_bytes_for_si(struct iio_dev *indio_dev,
-					     unsigned int scan_index)
+static int iio_storage_bytes_for_si(struct iio_dev *indio_dev,
+				    unsigned int scan_index)
 {
 	const struct iio_chan_spec *ch;
 	const struct iio_scan_type *scan_type;
 	unsigned int bytes;
 
 	ch = iio_find_channel_from_si(indio_dev, scan_index);
-	scan_type = &ch->scan_type;
+	scan_type = iio_get_current_scan_type(indio_dev, ch);
+	if (IS_ERR(scan_type))
+		return PTR_ERR(scan_type);
+
 	bytes = scan_type->storagebits / 8;
 
 	if (scan_type->repeat > 1)
@@ -708,7 +718,7 @@ static unsigned int iio_storage_bytes_for_si(struct iio_dev *indio_dev,
 	return bytes;
 }
 
-static unsigned int iio_storage_bytes_for_timestamp(struct iio_dev *indio_dev)
+static int iio_storage_bytes_for_timestamp(struct iio_dev *indio_dev)
 {
 	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
 
@@ -726,6 +736,9 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
 	for_each_set_bit(i, mask,
 			 indio_dev->masklength) {
 		length = iio_storage_bytes_for_si(indio_dev, i);
+		if (length < 0)
+			return length;
+
 		bytes = ALIGN(bytes, length);
 		bytes += length;
 		largest = max(largest, length);
@@ -733,6 +746,9 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
 
 	if (timestamp) {
 		length = iio_storage_bytes_for_timestamp(indio_dev);
+		if (length < 0)
+			return length;
+
 		bytes = ALIGN(bytes, length);
 		bytes += length;
 		largest = max(largest, length);
@@ -1012,14 +1028,22 @@ static int iio_buffer_update_demux(struct iio_dev *indio_dev,
 				       indio_dev->masklength,
 				       in_ind + 1);
 		while (in_ind != out_ind) {
-			length = iio_storage_bytes_for_si(indio_dev, in_ind);
+			ret = iio_storage_bytes_for_si(indio_dev, in_ind);
+			if (ret < 0)
+				goto error_clear_mux_table;
+
+			length = ret;
 			/* Make sure we are aligned */
 			in_loc = roundup(in_loc, length) + length;
 			in_ind = find_next_bit(indio_dev->active_scan_mask,
 					       indio_dev->masklength,
 					       in_ind + 1);
 		}
-		length = iio_storage_bytes_for_si(indio_dev, in_ind);
+		ret = iio_storage_bytes_for_si(indio_dev, in_ind);
+		if (ret < 0)
+			goto error_clear_mux_table;
+
+		length = ret;
 		out_loc = roundup(out_loc, length);
 		in_loc = roundup(in_loc, length);
 		ret = iio_buffer_add_demux(buffer, &p, in_loc, out_loc, length);
@@ -1030,7 +1054,11 @@ static int iio_buffer_update_demux(struct iio_dev *indio_dev,
 	}
 	/* Relies on scan_timestamp being last */
 	if (buffer->scan_timestamp) {
-		length = iio_storage_bytes_for_timestamp(indio_dev);
+		ret = iio_storage_bytes_for_timestamp(indio_dev);
+		if (ret < 0)
+			goto error_clear_mux_table;
+
+		length = ret;
 		out_loc = roundup(out_loc, length);
 		in_loc = roundup(in_loc, length);
 		ret = iio_buffer_add_demux(buffer, &p, in_loc, out_loc, length);
@@ -1597,6 +1625,22 @@ static long iio_device_buffer_ioctl(struct iio_dev *indio_dev, struct file *filp
 	}
 }
 
+static int iio_channel_validate_scan_type(struct device *dev, int ch,
+					  const struct iio_scan_type *scan_type)
+{
+	/* Verify that sample bits fit into storage */
+	if (scan_type->storagebits < scan_type->realbits + scan_type->shift) {
+		dev_err(dev,
+			"Channel %d storagebits (%d) < shifted realbits (%d + %d)\n",
+			ch, scan_type->storagebits,
+			scan_type->realbits,
+			scan_type->shift);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
 					     struct iio_dev *indio_dev,
 					     int index)
@@ -1626,18 +1670,33 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
 			if (channels[i].scan_index < 0)
 				continue;
 
-			scan_type = &channels[i].scan_type;
-
-			/* Verify that sample bits fit into storage */
-			if (scan_type->storagebits <
-			    scan_type->realbits + scan_type->shift) {
-				dev_err(&indio_dev->dev,
-					"Channel %d storagebits (%d) < shifted realbits (%d + %d)\n",
-					i, scan_type->storagebits,
-					scan_type->realbits,
-					scan_type->shift);
-				ret = -EINVAL;
-				goto error_cleanup_dynamic;
+			if (channels[i].has_ext_scan_type) {
+				int j;
+
+				/*
+				 * get_current_scan_type is required when using
+				 * extended scan types.
+				 */
+				if (!indio_dev->info->get_current_scan_type) {
+					ret = -EINVAL;
+					goto error_cleanup_dynamic;
+				}
+
+				for (j = 0; j < channels[i].num_ext_scan_type; j++) {
+					scan_type = &channels[i].ext_scan_type[j];
+
+					ret = iio_channel_validate_scan_type(
+						&indio_dev->dev, i, scan_type);
+					if (ret)
+						goto error_cleanup_dynamic;
+				}
+			} else {
+				scan_type = &channels[i].scan_type;
+
+				ret = iio_channel_validate_scan_type(
+						&indio_dev->dev, i, scan_type);
+				if (ret)
+					goto error_cleanup_dynamic;
 			}
 
 			ret = iio_buffer_add_channel_sysfs(indio_dev, buffer,