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>

Author: dlech

drivers/iio/industrialio-buffer.c

@@ -399,9 +399,16 @@ 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
@@ -732,24 +739,20 @@ 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;
-	bytes = scan_type->storagebits / 8;
-
-	if (scan_type->repeat > 1)
-		bytes *= scan_type->repeat;
-
+	bytes = ch->scan_type.storagebits / 8;
+	if (ch->scan_type.repeat > 1)
+		bytes *= ch->scan_type.repeat;
 	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);
 
@@ -767,13 +770,19 @@ 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);
 	}
 
 	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);
@@ -1052,14 +1061,22 @@ 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);
@@ -1070,7 +1087,11 @@ 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);
@@ -1899,16 +1920,14 @@ 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);
+					i, channels[i].scan_type.storagebits,
+					channels[i].scan_type.realbits,
+					channels[i].scan_type.shift);
 				ret = -EINVAL;
 				goto error_cleanup_dynamic;
 			}

include/linux/iio/iio.h

@@ -204,7 +204,13 @@ struct iio_scan_type {
  * @address:		Driver specific identifier.
  * @scan_index:		Monotonic index to give ordering in scans when read
  *			from a buffer.
- * @scan_type:		struct describing the scan type
+ * @scan_type:		struct describing the scan type - mutually exclusive
+ *			with ext_scan_type.
+ * @ext_scan_type:	Used in rare cases where there is more than one scan
+ *			format for a channel. When this is used, the flag
+ *			has_ext_scan_type must be set and the driver must
+ *			implement get_current_scan_type in struct iio_info.
+ * @num_ext_scan_type:	Number of elements in ext_scan_type.
  * @info_mask_separate: What information is to be exported that is specific to
  *			this channel.
  * @info_mask_separate_available: What availability information is to be
@@ -245,14 +251,21 @@ struct iio_scan_type {
  *			attributes but not for event codes.
  * @output:		Channel is output.
  * @differential:	Channel is differential.
+ * @has_ext_scan_type:	True if ext_scan_type is used instead of scan_type.
  */
 struct iio_chan_spec {
 	enum iio_chan_type	type;
 	int			channel;
 	int			channel2;
 	unsigned long		address;
 	int			scan_index;
-	struct iio_scan_type scan_type;
+	union {
+		struct iio_scan_type scan_type;
+		struct {
+			const struct iio_scan_type *ext_scan_type;
+			unsigned int num_ext_scan_type;
+		};
+	};
 	long			info_mask_separate;
 	long			info_mask_separate_available;
 	long			info_mask_shared_by_type;
@@ -270,6 +283,7 @@ struct iio_chan_spec {
 	unsigned		indexed:1;
 	unsigned		output:1;
 	unsigned		differential:1;
+	unsigned		has_ext_scan_type:1;
 };
 
 
@@ -427,6 +441,9 @@ struct iio_trigger; /* forward declaration */
  *			for better event identification.
  * @validate_trigger:	function to validate the trigger when the
  *			current trigger gets changed.
+ * @get_current_scan_type: must be implemented by drivers that use ext_scan_type
+ *			in the channel spec to return the index of the currently
+ *			active ext_scan type for a channel.
  * @update_scan_mode:	function to configure device and scan buffer when
  *			channels have changed
  * @debugfs_reg_access:	function to read or write register value of device
@@ -517,6 +534,8 @@ struct iio_info {
 
 	int (*validate_trigger)(struct iio_dev *indio_dev,
 				struct iio_trigger *trig);
+	int (*get_current_scan_type)(const struct iio_dev *indio_dev,
+				     const struct iio_chan_spec *chan);
 	int (*update_scan_mode)(struct iio_dev *indio_dev,
 				const unsigned long *scan_mask);
 	int (*debugfs_reg_access)(struct iio_dev *indio_dev,
@@ -787,6 +806,38 @@ static inline struct dentry *iio_get_debugfs_dentry(struct iio_dev *indio_dev)
 }
 #endif
 
+/**
+ * iio_get_current_scan_type - Get the current scan type for a channel
+ * @indio_dev:	the IIO device to get the scan type for
+ * @chan:	the channel to get the scan type for
+ *
+ * Most devices only have one scan type per channel and can just access it
+ * directly without calling this function. Core IIO code and drivers that
+ * implement ext_scan_type in the channel spec should use this function to
+ * get the current scan type for a channel.
+ *
+ * Returns: the current scan type for the channel or error.
+ */
+static inline const struct iio_scan_type
+*iio_get_current_scan_type(const struct iio_dev *indio_dev,
+			   const struct iio_chan_spec *chan)
+{
+	int ret;
+
+	if (chan->has_ext_scan_type) {
+		ret = indio_dev->info->get_current_scan_type(indio_dev, chan);
+		if (ret < 0)
+			return ERR_PTR(ret);
+
+		if (ret >= chan->num_ext_scan_type)
+			return ERR_PTR(-EINVAL);
+
+		return &chan->ext_scan_type[ret];
+	}
+
+	return &chan->scan_type;
+}
+
 ssize_t iio_format_value(char *buf, unsigned int type, int size, int *vals);
 
 int iio_str_to_fixpoint(const char *str, int fract_mult, int *integer,