iio: buffer: introduce support for attaching more IIO buffers

With this change, calling iio_device_attach_buffer() will actually attach
more buffers.
Right now this doesn't do any validation of whether a buffer is attached
twice; maybe that can be added later (if needed). Attaching a buffer more
than once should yield noticeably bad results.

The first buffer is the legacy buffer, so a reference is kept to it.

At this point, accessing the data for the extra buffers (that are added
after the first one) isn't possible yet.

The iio_device_attach_buffer() is also changed to return an error code,
which for now is -ENOMEM if the array could not be realloc-ed for more
buffers.
To adapt to this new change iio_device_attach_buffer() is called last in
all place where it's called. The realloc failure is a bit difficult to
handle during un-managed calls when unwinding, so it's better to have this
as the last error in the setup_buffer calls.

At this point, no driver should call iio_device_attach_buffer() directly,
it should call one of the {devm_}iio_triggered_buffer_setup() or
devm_iio_kfifo_buffer_setup() or devm_iio_dmaengine_buffer_setup()
functions. This makes iio_device_attach_buffer() a bit easier to handle.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210215104043.91251-20-alexandru.ardelean@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

3 files changed, 9 insertions, 2 deletions

diff --git a/include/linux/iio/buffer.h b/include/linux/iio/buffer.h
index 8febc23f5f26..b6928ac5c63d 100644
--- a/include/linux/iio/buffer.h
+++ b/include/linux/iio/buffer.h
@@ -41,7 +41,7 @@ static inline int iio_push_to_buffers_with_timestamp(struct iio_dev *indio_dev,
 bool iio_validate_scan_mask_onehot(struct iio_dev *indio_dev,
 				   const unsigned long *mask);
 
-void iio_device_attach_buffer(struct iio_dev *indio_dev,
-			      struct iio_buffer *buffer);
+int iio_device_attach_buffer(struct iio_dev *indio_dev,
+			     struct iio_buffer *buffer);
 
 #endif /* _IIO_BUFFER_GENERIC_H_ */
diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
index 41044320e581..768b90c64412 100644
--- a/include/linux/iio/buffer_impl.h
+++ b/include/linux/iio/buffer_impl.h
@@ -112,6 +112,9 @@ struct iio_buffer {
 	/* @demux_bounce: Buffer for doing gather from incoming scan. */
 	void *demux_bounce;
 
+	/* @attached_entry: Entry in the devices list of buffers attached by the driver. */
+	struct list_head attached_entry;
+
 	/* @buffer_list: Entry in the devices list of current buffers. */
 	struct list_head buffer_list;
 
diff --git a/include/linux/iio/iio-opaque.h b/include/linux/iio/iio-opaque.h
index 1a9310b0145f..b6ebc04af3e7 100644
--- a/include/linux/iio/iio-opaque.h
+++ b/include/linux/iio/iio-opaque.h
@@ -7,6 +7,8 @@
  * struct iio_dev_opaque - industrial I/O device opaque information
  * @indio_dev:			public industrial I/O device information
  * @event_interface:		event chrdevs associated with interrupt lines
+ * @attached_buffers:		array of buffers statically attached by the driver
+ * @attached_buffers_cnt:	number of buffers in the array of statically attached buffers
  * @buffer_list:		list of all buffers currently attached
  * @channel_attr_list:		keep track of automatically created channel
  *				attributes
@@ -24,6 +26,8 @@
 struct iio_dev_opaque {
 	struct iio_dev			indio_dev;
 	struct iio_event_interface	*event_interface;
+	struct iio_buffer		**attached_buffers;
+	unsigned int			attached_buffers_cnt;
 	struct list_head		buffer_list;
 	struct list_head		channel_attr_list;
 	struct attribute_group		chan_attr_group;