iio: Add buffer enable/disable callbacks

This patch adds a enable and disable callback that is called when the
buffer is enabled/disabled. This can be used by buffer implementations that
need to do some setup or teardown work. E.g. a DMA based buffer can use
this to start/stop the DMA transfer.

Signed-off-by: Lars-Peter Clausen <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/industrialio-buffer.c

···
 		iio_buffer_deactivate(buffer);
 }
 
+static int iio_buffer_enable(struct iio_buffer *buffer,
+	struct iio_dev *indio_dev)
+{
+	if (!buffer->access->enable)
+		return 0;
+	return buffer->access->enable(buffer, indio_dev);
+}
+
+static int iio_buffer_disable(struct iio_buffer *buffer,
+	struct iio_dev *indio_dev)
+{
+	if (!buffer->access->disable)
+		return 0;
+	return buffer->access->disable(buffer, indio_dev);
+}
+
 static void iio_buffer_update_bytes_per_datum(struct iio_dev *indio_dev,
 	struct iio_buffer *buffer)
 {
···
 static int iio_enable_buffers(struct iio_dev *indio_dev,
 	struct iio_device_config *config)
 {
+	struct iio_buffer *buffer;
 	int ret;
 
 	indio_dev->active_scan_mask = config->scan_mask;
···
 		indio_dev->info->hwfifo_set_watermark(indio_dev,
 			config->watermark);
 
+	list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
+		ret = iio_buffer_enable(buffer, indio_dev);
+		if (ret)
+			goto err_disable_buffers;
+	}
+
 	indio_dev->currentmode = config->mode;
 
 	if (indio_dev->setup_ops->postenable) {
···
 		if (ret) {
 			dev_dbg(&indio_dev->dev,
 			       "Buffer not started: postenable failed (%d)\n", ret);
-			goto err_run_postdisable;
+			goto err_disable_buffers;
 		}
 	}
 
 	return 0;
 
+err_disable_buffers:
+	list_for_each_entry_continue_reverse(buffer, &indio_dev->buffer_list,
+					     buffer_list)
+		iio_buffer_disable(buffer, indio_dev);
 err_run_postdisable:
 	indio_dev->currentmode = INDIO_DIRECT_MODE;
 	if (indio_dev->setup_ops->postdisable)
···
 
 static int iio_disable_buffers(struct iio_dev *indio_dev)
 {
+	struct iio_buffer *buffer;
 	int ret = 0;
 	int ret2;
 
···
 
 	if (indio_dev->setup_ops->predisable) {
 		ret2 = indio_dev->setup_ops->predisable(indio_dev);
+		if (ret2 && !ret)
+			ret = ret2;
+	}
+
+	list_for_each_entry(buffer, &indio_dev->buffer_list, buffer_list) {
+		ret2 = iio_buffer_disable(buffer, indio_dev);
 		if (ret2 && !ret)
 			ret = ret2;
 	}

include/linux/iio/buffer.h

···
  *			storage.
  * @set_bytes_per_datum:set number of bytes per datum
  * @set_length:		set number of datums in buffer
+ * @enable:             called if the buffer is attached to a device and the
+ *                      device starts sampling. Calls are balanced with
+ *                      @disable.
+ * @disable:            called if the buffer is attached to a device and the
+ *                      device stops sampling. Calles are balanced with @enable.
  * @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
···
 
 	int (*set_bytes_per_datum)(struct iio_buffer *buffer, size_t bpd);
 	int (*set_length)(struct iio_buffer *buffer, int length);
+
+	int (*enable)(struct iio_buffer *buffer, struct iio_dev *indio_dev);
+	int (*disable)(struct iio_buffer *buffer, struct iio_dev *indio_dev);
 
 	void (*release)(struct iio_buffer *buffer);