[dma] Move I/O buffer DMA operations to iobuf.h

Include a potential DMA mapping within the definition of an I/O
buffer, and move all I/O buffer DMA mapping functions from dma.h to
iobuf.h.  This avoids the need for drivers to maintain a separate list
of DMA mappings for each I/O buffer that they may handle.

Network device drivers typically do not keep track of transmit I/O
buffers, since the network device core already maintains a transmit
queue.  Drivers will typically call netdev_tx_complete_next() to
complete a transmission without first obtaining the relevant I/O
buffer pointer (and will rely on the network device core automatically
cancelling any pending transmissions when the device is closed).

To allow this driver design approach to be retained, update the
netdev_tx_complete() family of functions to automatically perform the
DMA unmapping operation if required.  For symmetry, also update the
netdev_rx() family of functions to behave the same way.

As a further convenience for drivers, allow the network device core to
automatically perform DMA mapping on the transmit datapath before
calling the driver's transmit() method.  This avoids the need to
introduce a mapping error handling code path into the typically
error-free transmit methods.

With these changes, the modifications required to update a typical
network device driver to use the new DMA API are fairly minimal:

- Allocate and free descriptor rings and similar coherent structures
  using dma_alloc()/dma_free() rather than malloc_phys()/free_phys()

- Allocate and free receive buffers using alloc_rx_iob()/free_rx_iob()
  rather than alloc_iob()/free_iob()

- Calculate DMA addresses using dma() or iob_dma() rather than
  virt_to_bus()

- Set a 64-bit DMA mask if needed using dma_set_mask_64bit() and
  thereafter eliminate checks on DMA address ranges

- Either record the DMA device in netdev->dma, or call iob_map_tx() as
  part of the transmit() method

- Ensure that debug messages use virt_to_phys() when displaying
  "hardware" addresses

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/dma.c

@@ -25,7 +25,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <assert.h>
 #include <errno.h>
-#include <ipxe/iobuf.h>
 #include <ipxe/dma.h>
 
 /** @file
@@ -139,43 +138,3 @@ PROVIDE_DMAAPI ( op, dma_alloc, dma_op_alloc );
 PROVIDE_DMAAPI ( op, dma_free, dma_op_free );
 PROVIDE_DMAAPI ( op, dma_set_mask, dma_op_set_mask );
 PROVIDE_DMAAPI_INLINE ( op, dma_phys );
-
-/******************************************************************************
- *
- * Utility functions
- *
- ******************************************************************************
- */
-
-/**
- * Allocate and map I/O buffer for receiving data from device
- *
- * @v dma		DMA device
- * @v map		DMA mapping to fill in
- * @v len		Length of I/O buffer
- * @ret iobuf		I/O buffer, or NULL on error
- */
-struct io_buffer * dma_alloc_rx_iob ( struct dma_device *dma,
-				      struct dma_mapping *map,
-				      size_t len ) {
-	struct io_buffer *iobuf;
-	int rc;
-
-	/* Allocate I/O buffer */
-	iobuf = alloc_iob ( len );
-	if ( ! iobuf )
-		goto err_alloc;
-
-	/* Map I/O buffer */
-	if ( ( rc = dma_map ( dma, map, virt_to_phys ( iobuf->data ),
-			      len, DMA_RX ) ) != 0 )
-		goto err_map;
-
-	return iobuf;
-
-	dma_unmap ( map );
- err_map:
-	free_iob ( iobuf );
- err_alloc:
-	return NULL;
-}

src/core/iobuf.c

@@ -110,6 +110,7 @@ struct io_buffer * alloc_iob_raw ( size_t len, size_t align, size_t offset ) {
 	}
 
 	/* Populate descriptor */
+	memset ( &iobuf->map, 0, sizeof ( iobuf->map ) );
 	iobuf->head = iobuf->data = iobuf->tail = data;
 	iobuf->end = ( data + len );
 
@@ -153,6 +154,7 @@ void free_iob ( struct io_buffer *iobuf ) {
 	assert ( iobuf->head <= iobuf->data );
 	assert ( iobuf->data <= iobuf->tail );
 	assert ( iobuf->tail <= iobuf->end );
+	assert ( ! dma_mapped ( &iobuf->map ) );
 
 	/* Free buffer */
 	len = ( iobuf->end - iobuf->head );
@@ -169,6 +171,49 @@ void free_iob ( struct io_buffer *iobuf ) {
 	}
 }
 
+/**
+ * Allocate and map I/O buffer for receive DMA
+ *
+ * @v len		Length of I/O buffer
+ * @v dma		DMA device
+ * @ret iobuf		I/O buffer, or NULL on error
+ */
+struct io_buffer * alloc_rx_iob ( size_t len, struct dma_device *dma ) {
+	struct io_buffer *iobuf;
+	int rc;
+
+	/* Allocate I/O buffer */
+	iobuf = alloc_iob ( len );
+	if ( ! iobuf )
+		goto err_alloc;
+
+	/* Map I/O buffer */
+	if ( ( rc = iob_map_rx ( iobuf, dma ) ) != 0 )
+		goto err_map;
+
+	return iobuf;
+
+	iob_unmap ( iobuf );
+ err_map:
+	free_iob ( iobuf );
+ err_alloc:
+	return NULL;
+}
+
+/**
+ * Unmap and free I/O buffer for receive DMA
+ *
+ * @v iobuf	I/O buffer
+ */
+void free_rx_iob ( struct io_buffer *iobuf ) {
+
+	/* Unmap I/O buffer */
+	iob_unmap ( iobuf );
+
+	/* Free I/O buffer */
+	free_iob ( iobuf );
+}
+
 /**
  * Ensure I/O buffer has sufficient headroom
  *