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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/buffer/industrialio-buffer-dmaengine.c

···
 
 	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
 
-	iio_device_attach_buffer(indio_dev, buffer);
-
-	return 0;
+	return iio_device_attach_buffer(indio_dev, buffer);
 }
 EXPORT_SYMBOL_GPL(devm_iio_dmaengine_buffer_setup);
 

drivers/iio/buffer/industrialio-triggered-buffer.c

···
 		goto error_ret;
 	}
 
-	iio_device_attach_buffer(indio_dev, buffer);
-
 	indio_dev->pollfunc = iio_alloc_pollfunc(h,
 						 thread,
 						 IRQF_ONESHOT,
···
 
 	buffer->attrs = buffer_attrs;
 
+	ret = iio_device_attach_buffer(indio_dev, buffer);
+	if (ret < 0)
+		goto error_dealloc_pollfunc;
+
 	return 0;
 
+error_dealloc_pollfunc:
+	iio_dealloc_pollfunc(indio_dev->pollfunc);
 error_kfifo_free:
-	iio_kfifo_free(indio_dev->buffer);
+	iio_kfifo_free(buffer);
 error_ret:
 	return ret;
 }

drivers/iio/buffer/kfifo_buf.c

···
 	if (!buffer)
 		return -ENOMEM;
 
-	iio_device_attach_buffer(indio_dev, buffer);
-
 	indio_dev->modes |= mode_flags;
 	indio_dev->setup_ops = setup_ops;
 
-	return 0;
+	return iio_device_attach_buffer(indio_dev, buffer);
 }
 EXPORT_SYMBOL_GPL(devm_iio_kfifo_buffer_setup);
 

drivers/iio/iio_core.h

···
 ssize_t iio_buffer_read_outer(struct file *filp, char __user *buf,
 			      size_t n, loff_t *f_ps);
 
-int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev);
-void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev);
+int iio_buffers_alloc_sysfs_and_mask(struct iio_dev *indio_dev);
+void iio_buffers_free_sysfs_and_mask(struct iio_dev *indio_dev);
 
 #define iio_buffer_poll_addr (&iio_buffer_poll)
 #define iio_buffer_read_outer_addr (&iio_buffer_read_outer)
 
 void iio_disable_all_buffers(struct iio_dev *indio_dev);
 void iio_buffer_wakeup_poll(struct iio_dev *indio_dev);
+void iio_buffers_put(struct iio_dev *indio_dev);
 
 #else
 
 #define iio_buffer_poll_addr NULL
 #define iio_buffer_read_outer_addr NULL
 
-static inline int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
+static inline int iio_buffers_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
 {
 	return 0;
 }
 
-static inline void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev) {}
+static inline void iio_buffers_free_sysfs_and_mask(struct iio_dev *indio_dev) {}
 
 static inline void iio_disable_all_buffers(struct iio_dev *indio_dev) {}
 static inline void iio_buffer_wakeup_poll(struct iio_dev *indio_dev) {}
+static inline void iio_buffers_put(struct iio_dev *indio_dev) {}
 
 #endif
 

drivers/iio/industrialio-buffer.c

···
  */
 void iio_buffer_wakeup_poll(struct iio_dev *indio_dev)
 {
-	struct iio_buffer *buffer = indio_dev->buffer;
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+	struct iio_buffer *buffer;
+	unsigned int i;
 
-	if (!buffer)
-		return;
-
-	wake_up(&buffer->pollq);
+	for (i = 0; i < iio_dev_opaque->attached_buffers_cnt; i++) {
+		buffer = iio_dev_opaque->attached_buffers[i];
+		wake_up(&buffer->pollq);
+	}
 }
 
 void iio_buffer_init(struct iio_buffer *buffer)
···
 		buffer->watermark = 1;
 }
 EXPORT_SYMBOL(iio_buffer_init);
+
+void iio_buffers_put(struct iio_dev *indio_dev)
+{
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+	struct iio_buffer *buffer;
+	unsigned int i;
+
+	for (i = 0; i < iio_dev_opaque->attached_buffers_cnt; i++) {
+		buffer = iio_dev_opaque->attached_buffers[i];
+		iio_buffer_put(buffer);
+	}
+}
 
 static ssize_t iio_show_scan_index(struct device *dev,
 				   struct device_attribute *attr,
···
 	iio_free_chan_devattr_list(&buffer->buffer_attr_list);
 }
 
-int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
+int iio_buffers_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
 {
-	struct iio_buffer *buffer = indio_dev->buffer;
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
 	const struct iio_chan_spec *channels;
-	int i;
+	struct iio_buffer *buffer;
+	int unwind_idx;
+	int ret, i;
 
 	channels = indio_dev->channels;
 	if (channels) {
···
 		indio_dev->masklength = ml;
 	}
 
-	if (!buffer)
+	if (!iio_dev_opaque->attached_buffers_cnt)
 		return 0;
 
-	return __iio_buffer_alloc_sysfs_and_mask(buffer, indio_dev, 0);
+	for (i = 0; i < iio_dev_opaque->attached_buffers_cnt; i++) {
+		buffer = iio_dev_opaque->attached_buffers[i];
+		ret = __iio_buffer_alloc_sysfs_and_mask(buffer, indio_dev, i);
+		if (ret) {
+			unwind_idx = i;
+			goto error_unwind_sysfs_and_mask;
+		}
+	}
+
+	return 0;
+
+error_unwind_sysfs_and_mask:
+	for (; unwind_idx >= 0; unwind_idx--) {
+		buffer = iio_dev_opaque->attached_buffers[unwind_idx];
+		__iio_buffer_free_sysfs_and_mask(buffer);
+	}
+	kfree(iio_dev_opaque->attached_buffers);
+	return ret;
 }
 
-void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
+void iio_buffers_free_sysfs_and_mask(struct iio_dev *indio_dev)
 {
-	struct iio_buffer *buffer = indio_dev->buffer;
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+	struct iio_buffer *buffer;
+	int i;
 
-	if (!buffer)
+	if (!iio_dev_opaque->attached_buffers_cnt)
 		return;
 
 	iio_buffer_unregister_legacy_sysfs_groups(indio_dev);
 
-	__iio_buffer_free_sysfs_and_mask(buffer);
+	for (i = iio_dev_opaque->attached_buffers_cnt - 1; i >= 0; i--) {
+		buffer = iio_dev_opaque->attached_buffers[i];
+		__iio_buffer_free_sysfs_and_mask(buffer);
+	}
+
+	kfree(iio_dev_opaque->attached_buffers);
 }
 
 /**
···
  * @indio_dev: The device the buffer should be attached to
  * @buffer: The buffer to attach to the device
  *
+ * Return 0 if successful, negative if error.
+ *
  * This function attaches a buffer to a IIO device. The buffer stays attached to
- * the device until the device is freed. The function should only be called at
- * most once per device.
+ * the device until the device is freed. For legacy reasons, the first attached
+ * buffer will also be assigned to 'indio_dev->buffer'.
  */
-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)
 {
-	indio_dev->buffer = iio_buffer_get(buffer);
+	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
+	struct iio_buffer **new, **old = iio_dev_opaque->attached_buffers;
+	unsigned int cnt = iio_dev_opaque->attached_buffers_cnt;
+
+	cnt++;
+
+	new = krealloc(old, sizeof(*new) * cnt, GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+	iio_dev_opaque->attached_buffers = new;
+
+	buffer = iio_buffer_get(buffer);
+
+	/* first buffer is legacy; attach it to the IIO device directly */
+	if (!indio_dev->buffer)
+		indio_dev->buffer = buffer;
+
+	iio_dev_opaque->attached_buffers[cnt - 1] = buffer;
+	iio_dev_opaque->attached_buffers_cnt = cnt;
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(iio_device_attach_buffer);

drivers/iio/industrialio-core.c

···
 	iio_device_unregister_eventset(indio_dev);
 	iio_device_unregister_sysfs(indio_dev);
 
-	iio_buffer_put(indio_dev->buffer);
+	iio_buffers_put(indio_dev);
 
 	ida_simple_remove(&iio_ida, indio_dev->id);
 	kfree(iio_dev_opaque);
···
 
 	iio_device_register_debugfs(indio_dev);
 
-	ret = iio_buffer_alloc_sysfs_and_mask(indio_dev);
+	ret = iio_buffers_alloc_sysfs_and_mask(indio_dev);
 	if (ret) {
 		dev_err(indio_dev->dev.parent,
 			"Failed to create buffer sysfs interfaces\n");
···
 		indio_dev->setup_ops == NULL)
 		indio_dev->setup_ops = &noop_ring_setup_ops;
 
-	if (indio_dev->buffer)
+	if (iio_dev_opaque->attached_buffers_cnt)
 		cdev_init(&indio_dev->chrdev, &iio_buffer_fileops);
 	else if (iio_dev_opaque->event_interface)
 		cdev_init(&indio_dev->chrdev, &iio_event_fileops);
 
-	if (indio_dev->buffer || iio_dev_opaque->event_interface) {
+	if (iio_dev_opaque->attached_buffers_cnt || iio_dev_opaque->event_interface) {
 		indio_dev->dev.devt = MKDEV(MAJOR(iio_devt), indio_dev->id);
 		indio_dev->chrdev.owner = this_mod;
 	}
···
 error_free_sysfs:
 	iio_device_unregister_sysfs(indio_dev);
 error_buffer_free_sysfs:
-	iio_buffer_free_sysfs_and_mask(indio_dev);
+	iio_buffers_free_sysfs_and_mask(indio_dev);
 error_unreg_debugfs:
 	iio_device_unregister_debugfs(indio_dev);
 	return ret;
···
 
 	mutex_unlock(&indio_dev->info_exist_lock);
 
-	iio_buffer_free_sysfs_and_mask(indio_dev);
+	iio_buffers_free_sysfs_and_mask(indio_dev);
 }
 EXPORT_SYMBOL(iio_device_unregister);
 

include/linux/iio/buffer.h

···
 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_ */

include/linux/iio/buffer_impl.h

···
 	/* @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;
 

include/linux/iio/iio-opaque.h

···
  * 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
···
 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;