iio: buffer-dmaengine: split requesting DMA channel from allocating buffer

Refactor the IIO dmaengine buffer code to split requesting the DMA
channel from allocating the buffer. We want to be able to add a new
function where the IIO device driver manages the DMA channel, so these
two actions need to be separate.

To do this, calling dma_request_chan() is moved from
iio_dmaengine_buffer_alloc() to iio_dmaengine_buffer_setup_ext(). A new
__iio_dmaengine_buffer_setup_ext() helper function is added to simplify
error unwinding and will also be used by a new function in a later
patch.

iio_dmaengine_buffer_free() now only frees the buffer and does not
release the DMA channel. A new iio_dmaengine_buffer_teardown() function
is added to unwind everything done in iio_dmaengine_buffer_setup_ext().
This keeps things more symmetrical with obvious pairs alloc/free and
setup/teardown.

Calling dma_get_slave_caps() in iio_dmaengine_buffer_alloc() is moved so
that we can avoid any gotos for error unwinding.

[ADI tree: had to adjust for devm_iio_dmaengine_buffer_setup_with_ops]

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250207-dlech-mainline-spi-engine-offload-2-v8-8-e48a489be48c@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: dlech

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

@@ -135,7 +135,7 @@ static struct iio_buffer *axi_adc_request_buffer(struct iio_backend *back,
 static void axi_adc_free_buffer(struct iio_backend *back,
 				struct iio_buffer *buffer)
 {
-	iio_dmaengine_buffer_free(buffer);
+	iio_dmaengine_buffer_teardown(buffer);
 }
 
 static const struct regmap_config axi_adc_regmap_config = {

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

@@ -255,39 +255,31 @@ static const struct iio_dev_attr *iio_dmaengine_buffer_attrs[] = {
 
 /**
  * iio_dmaengine_buffer_alloc() - Allocate new buffer which uses DMAengine
- * @dev: DMA channel consumer device
- * @channel: DMA channel name, typically "rx".
+ * @chan: DMA channel.
  *
  * This allocates a new IIO buffer which internally uses the DMAengine framework
- * to perform its transfers. The parent device will be used to request the DMA
- * channel.
+ * to perform its transfers.
  *
  * 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,
-	const char *channel, const struct iio_dma_buffer_ops *ops, void *data)
+static struct iio_buffer *iio_dmaengine_buffer_alloc(struct dma_chan *chan,
+						     const struct iio_dma_buffer_ops *ops,
+						     void *data)
 {
 	struct dmaengine_buffer *dmaengine_buffer;
 	unsigned int width, src_width, dest_width;
 	struct dma_slave_caps caps;
-	struct dma_chan *chan;
 	int ret;
 
+	ret = dma_get_slave_caps(chan, &caps);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
 	dmaengine_buffer = kzalloc(sizeof(*dmaengine_buffer), GFP_KERNEL);
 	if (!dmaengine_buffer)
 		return ERR_PTR(-ENOMEM);
 
-	chan = dma_request_chan(dev, channel);
-	if (IS_ERR(chan)) {
-		ret = PTR_ERR(chan);
-		goto err_free;
-	}
-
-	ret = dma_get_slave_caps(chan, &caps);
-	if (ret < 0)
-		goto err_free;
-
 	/* Needs to be aligned to the maximum of the minimums */
 	if (caps.src_addr_widths)
 		src_width = __ffs(caps.src_addr_widths);
@@ -320,10 +312,6 @@ static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
 	dmaengine_buffer->queue.buffer.access = &iio_dmaengine_buffer_ops;
 
 	return &dmaengine_buffer->queue.buffer;
-
-err_free:
-	kfree(dmaengine_buffer);
-	return ERR_PTR(ret);
 }
 
 /**
@@ -332,17 +320,59 @@ static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
  *
  * Frees a buffer previously allocated with iio_dmaengine_buffer_alloc().
  */
-void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
+static void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
 {
 	struct dmaengine_buffer *dmaengine_buffer =
 		iio_buffer_to_dmaengine_buffer(buffer);
 
 	iio_dma_buffer_exit(&dmaengine_buffer->queue);
-	dma_release_channel(dmaengine_buffer->chan);
-
 	iio_buffer_put(buffer);
 }
-EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_free, IIO_DMAENGINE_BUFFER);
+
+/**
+ * iio_dmaengine_buffer_teardown() - Releases DMA channel and frees buffer
+ * @buffer: Buffer to free
+ *
+ * Releases the DMA channel and frees the buffer previously setup with
+ * iio_dmaengine_buffer_setup_ext().
+ */
+void iio_dmaengine_buffer_teardown(struct iio_buffer *buffer)
+{
+	struct dmaengine_buffer *dmaengine_buffer =
+		iio_buffer_to_dmaengine_buffer(buffer);
+	struct dma_chan *chan = dmaengine_buffer->chan;
+
+	iio_dmaengine_buffer_free(buffer);
+	dma_release_channel(chan);
+}
+EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_teardown, IIO_DMAENGINE_BUFFER);
+
+static struct iio_buffer
+*__iio_dmaengine_buffer_setup_ext(struct iio_dev *indio_dev,
+				  struct dma_chan *chan,
+				  enum iio_buffer_direction dir,
+				  const struct iio_dma_buffer_ops *ops,
+				  void *data)
+{
+	struct iio_buffer *buffer;
+	int ret;
+
+	buffer = iio_dmaengine_buffer_alloc(chan, ops, data);
+	if (IS_ERR(buffer))
+		return ERR_CAST(buffer);
+
+	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
+
+	buffer->direction = dir;
+
+	ret = iio_device_attach_buffer(indio_dev, buffer);
+	if (ret) {
+		iio_dmaengine_buffer_free(buffer);
+		return ERR_PTR(ret);
+	}
+
+	return buffer;
+}
 
 /**
  * iio_dmaengine_buffer_setup_ext() - Setup a DMA buffer for an IIO device
@@ -356,30 +386,24 @@ EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_free, IIO_DMAENGINE_BUFFER);
  * It also appends the INDIO_BUFFER_HARDWARE mode to the supported modes of the
  * IIO device.
  *
- * Once done using the buffer iio_dmaengine_buffer_free() should be used to
+ * Once done using the buffer iio_dmaengine_buffer_teardown() should be used to
  * release it.
  */
 struct iio_buffer *iio_dmaengine_buffer_setup_ext(struct device *dev,
 						  struct iio_dev *indio_dev,
 						  const char *channel,
 						  enum iio_buffer_direction dir)
 {
+	struct dma_chan *chan;
 	struct iio_buffer *buffer;
-	int ret;
-
-	buffer = iio_dmaengine_buffer_alloc(dev, channel, NULL, NULL);
-	if (IS_ERR(buffer))
-		return ERR_CAST(buffer);
-
-	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
 
-	buffer->direction = dir;
+	chan = dma_request_chan(dev, channel);
+	if (IS_ERR(chan))
+		return ERR_CAST(chan);
 
-	ret = iio_device_attach_buffer(indio_dev, buffer);
-	if (ret) {
-		iio_dmaengine_buffer_free(buffer);
-		return ERR_PTR(ret);
-	}
+	buffer = __iio_dmaengine_buffer_setup_ext(indio_dev, chan, dir, NULL, NULL);
+	if (IS_ERR(buffer))
+		dma_release_channel(chan);
 
 	return buffer;
 }
@@ -397,29 +421,23 @@ static struct iio_buffer
 				     const struct iio_dma_buffer_ops *ops,
 				     void *data)
 {
+	struct dma_chan *chan;
 	struct iio_buffer *buffer;
-	int ret;
-
-	buffer = iio_dmaengine_buffer_alloc(dev, channel, ops, data);
-	if (IS_ERR(buffer))
-		return ERR_CAST(buffer);
-
-	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
 
-	buffer->direction = dir;
+	chan = dma_request_chan(dev, channel);
+	if (IS_ERR(chan))
+		return ERR_CAST(chan);
 
-	ret = iio_device_attach_buffer(indio_dev, buffer);
-	if (ret) {
-		iio_dmaengine_buffer_free(buffer);
-		return ERR_PTR(ret);
-	}
+	buffer = __iio_dmaengine_buffer_setup_ext(indio_dev, chan, dir, ops, data);
+	if (IS_ERR(buffer))
+		dma_release_channel(chan);
 
 	return buffer;
 }
 
-static void __devm_iio_dmaengine_buffer_free(void *buffer)
+static void devm_iio_dmaengine_buffer_teardown(void *buffer)
 {
-	iio_dmaengine_buffer_free(buffer);
+	iio_dmaengine_buffer_teardown(buffer);
 }
 
 /**
@@ -445,7 +463,7 @@ int devm_iio_dmaengine_buffer_setup_ext(struct device *dev,
 	if (IS_ERR(buffer))
 		return PTR_ERR(buffer);
 
-	return devm_add_action_or_reset(dev, __devm_iio_dmaengine_buffer_free,
+	return devm_add_action_or_reset(dev, devm_iio_dmaengine_buffer_teardown,
 					buffer);
 }
 EXPORT_SYMBOL_NS_GPL(devm_iio_dmaengine_buffer_setup_ext, IIO_DMAENGINE_BUFFER);
@@ -468,7 +486,7 @@ int devm_iio_dmaengine_buffer_setup_with_ops(struct device *dev,
 	if (IS_ERR(buffer))
 		return PTR_ERR(buffer);
 
-	return devm_add_action_or_reset(dev, __devm_iio_dmaengine_buffer_free,
+	return devm_add_action_or_reset(dev, devm_iio_dmaengine_buffer_teardown,
 					buffer);
 }
 EXPORT_SYMBOL_NS_GPL(devm_iio_dmaengine_buffer_setup_with_ops, IIO_DMAENGINE_BUFFER);

include/linux/iio/buffer-dmaengine.h

@@ -20,7 +20,7 @@ int iio_dmaengine_buffer_submit_block(struct iio_dma_buffer_queue *queue,
 	struct iio_dma_buffer_block *block);
 void iio_dmaengine_buffer_abort(struct iio_dma_buffer_queue *queue);
 
-void iio_dmaengine_buffer_free(struct iio_buffer *buffer);
+void iio_dmaengine_buffer_teardown(struct iio_buffer *buffer);
 struct iio_buffer *iio_dmaengine_buffer_setup_ext(struct device *dev,
 						  struct iio_dev *indio_dev,
 						  const char *channel,