iio: Specify supported modes for buffers

For each buffer type specify the supported device modes for this buffer.
This allows us for devices which support multiple different operating modes
to pick the correct operating mode based on the modes supported by the
attached buffers.

It also prevents that buffers with conflicting modes are attached
to a device at the same time or that a buffer with a non-supported mode is
attached to a device (e.g. in-kernel callback buffer to a device only
supporting hardware mode).

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/buffer_cb.c

@@ -33,6 +33,8 @@ static void iio_buffer_cb_release(struct iio_buffer *buffer)
 static const struct iio_buffer_access_funcs iio_cb_access = {
 	.store_to = &iio_buffer_cb_store_to,
 	.release = &iio_buffer_cb_release,
+
+	.modes = INDIO_BUFFER_SOFTWARE | INDIO_BUFFER_TRIGGERED,
 };
 
 struct iio_cb_buffer *iio_channel_get_all_cb(struct device *dev,

drivers/iio/industrialio-buffer.c

@@ -604,6 +604,7 @@ static int iio_verify_update(struct iio_dev *indio_dev,
 	const unsigned long *scan_mask;
 	struct iio_buffer *buffer;
 	bool scan_timestamp;
+	unsigned int modes;
 
 	memset(config, 0, sizeof(*config));
 
@@ -615,12 +616,23 @@ static int iio_verify_update(struct iio_dev *indio_dev,
 		list_is_singular(&indio_dev->buffer_list))
 			return 0;
 
+	modes = indio_dev->modes;
+
+	list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
+		if (buffer == remove_buffer)
+			continue;
+		modes &= buffer->access->modes;
+	}
+
+	if (insert_buffer)
+		modes &= insert_buffer->access->modes;
+
 	/* Definitely possible for devices to support both of these. */
-	if ((indio_dev->modes & INDIO_BUFFER_TRIGGERED) && indio_dev->trig) {
+	if ((modes & INDIO_BUFFER_TRIGGERED) && indio_dev->trig) {
 		config->mode = INDIO_BUFFER_TRIGGERED;
-	} else if (indio_dev->modes & INDIO_BUFFER_HARDWARE) {
+	} else if (modes & INDIO_BUFFER_HARDWARE) {
 		config->mode = INDIO_BUFFER_HARDWARE;
-	} else if (indio_dev->modes & INDIO_BUFFER_SOFTWARE) {
+	} else if (modes & INDIO_BUFFER_SOFTWARE) {
 		config->mode = INDIO_BUFFER_SOFTWARE;
 	} else {
 		/* Can only occur on first buffer */

drivers/iio/kfifo_buf.c

@@ -135,6 +135,8 @@ static const struct iio_buffer_access_funcs kfifo_access_funcs = {
 	.set_bytes_per_datum = &iio_set_bytes_per_datum_kfifo,
 	.set_length = &iio_set_length_kfifo,
 	.release = &iio_kfifo_buffer_release,
+
+	.modes = INDIO_BUFFER_SOFTWARE | INDIO_BUFFER_TRIGGERED,
 };
 
 struct iio_buffer *iio_kfifo_allocate(void)

drivers/staging/iio/accel/sca3000_ring.c

@@ -258,6 +258,8 @@ static const struct iio_buffer_access_funcs sca3000_ring_access_funcs = {
 	.read_first_n = &sca3000_read_first_n_hw_rb,
 	.data_available = sca3000_ring_buf_data_available,
 	.release = sca3000_ring_release,
+
+	.modes = INDIO_BUFFER_HARDWARE,
 };
 
 int sca3000_configure_ring(struct iio_dev *indio_dev)

include/linux/iio/buffer.h

@@ -29,6 +29,7 @@ struct iio_buffer;
  * @set_length:		set number of datums in buffer
  * @release:		called when the last reference to the buffer is dropped,
  *			should free all resources allocated by the buffer.
+ * @modes:		Supported operating modes by this buffer type
  *
  * The purpose of this structure is to make the buffer element
  * modular as event for a given driver, different usecases may require
@@ -51,6 +52,8 @@ struct iio_buffer_access_funcs {
 	int (*set_length)(struct iio_buffer *buffer, int length);
 
 	void (*release)(struct iio_buffer *buffer);
+
+	unsigned int modes;
 };
 
 /**