IIO: consumer: allow to set buffer sizes

Add iio consumer API to set buffer size and watermark according
to sysfs API.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

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

@@ -104,6 +104,17 @@ error_free_cb_buff:
 }
 EXPORT_SYMBOL_GPL(iio_channel_get_all_cb);
 
+int iio_channel_cb_set_buffer_watermark(struct iio_cb_buffer *cb_buff,
+					size_t watermark)
+{
+	if (!watermark)
+		return -EINVAL;
+	cb_buff->buffer.watermark = watermark;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(iio_channel_cb_set_buffer_watermark);
+
 int iio_channel_start_all_cb(struct iio_cb_buffer *cb_buff)
 {
 	return iio_update_buffers(cb_buff->indio_dev, &cb_buff->buffer,

include/linux/iio/consumer.h

@@ -133,6 +133,17 @@ struct iio_cb_buffer *iio_channel_get_all_cb(struct device *dev,
 					     int (*cb)(const void *data,
 						       void *private),
 					     void *private);
+/**
+ * iio_channel_cb_set_buffer_watermark() - set the buffer watermark.
+ * @cb_buffer:		The callback buffer from whom we want the channel
+ *			information.
+ * @watermark: buffer watermark in bytes.
+ *
+ * This function allows to configure the buffer watermark.
+ */
+int iio_channel_cb_set_buffer_watermark(struct iio_cb_buffer *cb_buffer,
+					size_t watermark);
+
 /**
  * iio_channel_release_all_cb() - release and unregister the callback.
  * @cb_buffer:		The callback buffer that was allocated.