iio: buffer-dmaengine: export buffer alloc and free functions

Export iio_dmaengine_buffer_free() and iio_dmaengine_buffer_alloc().
This is in preparation of introducing IIO backends support. This will
allow us to allocate a buffer and control it's lifetime from a device
different from the one holding the DMA firmware properties. Effectively,
in this case the struct device holding the firmware information about
the DMA channels is not the same as iio_dev->dev.parent (typical case).

While at it, namespace the buffer-dmaengine exports and update the
current user of these buffers.

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

drivers/iio/adc/adi-axi-adc.c

···
 MODULE_AUTHOR("Michael Hennerich <[e-mail]>");
 MODULE_DESCRIPTION("Analog Devices Generic AXI ADC IP core driver");
 MODULE_LICENSE("GPL v2");
+MODULE_IMPORT_NS(IIO_DMAENGINE_BUFFER);

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

···
  * Once done using the buffer iio_dmaengine_buffer_free() should be used to
  * release it.
  */
-static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
+struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
 	const char *channel)
 {
 	struct dmaengine_buffer *dmaengine_buffer;
···
 	kfree(dmaengine_buffer);
 	return ERR_PTR(ret);
 }
+EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_alloc, IIO_DMAENGINE_BUFFER);
 
 /**
  * iio_dmaengine_buffer_free() - Free dmaengine buffer
···
  *
  * Frees a buffer previously allocated with iio_dmaengine_buffer_alloc().
  */
-static void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
+void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
 {
 	struct dmaengine_buffer *dmaengine_buffer =
 		iio_buffer_to_dmaengine_buffer(buffer);
···
 
 	iio_buffer_put(buffer);
 }
+EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_free, IIO_DMAENGINE_BUFFER);
 
 static void __devm_iio_dmaengine_buffer_free(void *buffer)
 {
···
 
 	return iio_device_attach_buffer(indio_dev, buffer);
 }
-EXPORT_SYMBOL_GPL(devm_iio_dmaengine_buffer_setup);
+EXPORT_SYMBOL_NS_GPL(devm_iio_dmaengine_buffer_setup, IIO_DMAENGINE_BUFFER);
 
 MODULE_AUTHOR("Lars-Peter Clausen <[e-mail]>");
 MODULE_DESCRIPTION("DMA buffer for the IIO framework");

include/linux/iio/buffer-dmaengine.h

···
 struct iio_dev;
 struct device;
 
+struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
+					      const char *channel);
+void iio_dmaengine_buffer_free(struct iio_buffer *buffer);
 int devm_iio_dmaengine_buffer_setup(struct device *dev,
 				    struct iio_dev *indio_dev,
 				    const char *channel);