To get the dma_ API, you must #include <linux/dma-mapping.h>. This
provides dma_addr_t and the interfaces described below.
-A dma_addr_t can hold any valid DMA or bus address for the platform. It
-can be given to a device to use as a DMA source or target. A CPU cannot
-reference a dma_addr_t directly because there may be translation between
-its physical address space and the bus address space.
+A dma_addr_t can hold any valid DMA address for the platform. It can be
+given to a device to use as a DMA source or target. A CPU cannot reference
+a dma_addr_t directly because there may be translation between its physical
+address space and the DMA address space.
Part Ia - Using large DMA-coherent buffers
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address space) or NULL if the allocation failed.
It also returns a <dma_handle> which may be cast to an unsigned integer the
-same width as the bus and given to the device as the bus address base of
+same width as the bus and given to the device as the DMA address base of
the region.
Note: consistent memory can be expensive on some platforms, and the
enum dma_data_direction direction)
Maps a piece of processor virtual memory so it can be accessed by the
-device and returns the bus address of the memory.
+device and returns the DMA address of the memory.
The direction for both APIs may be converted freely by casting.
However the dma_ API uses a strongly typed enumerator for its
this API should be obtained from sources which guarantee it to be
physically contiguous (like kmalloc).
-Further, the bus address of the memory must be within the
+Further, the DMA address of the memory must be within the
dma_mask of the device (the dma_mask is a bit mask of the
-addressable region for the device, i.e., if the bus address of
-the memory ANDed with the dma_mask is still equal to the bus
+addressable region for the device, i.e., if the DMA address of
+the memory ANDed with the dma_mask is still equal to the DMA
address, then the device can perform DMA to the memory). To
ensure that the memory allocated by kmalloc is within the dma_mask,
the driver may specify various platform-dependent flags to restrict
-the bus address range of the allocation (e.g., on x86, GFP_DMA
-guarantees to be within the first 16MB of available bus addresses,
+the DMA address range of the allocation (e.g., on x86, GFP_DMA
+guarantees to be within the first 16MB of available DMA addresses,
as required by ISA devices).
Note also that the above constraints on physical contiguity and
dma_mask may not apply if the platform has an IOMMU (a device which
-maps an I/O bus address to a physical memory address). However, to be
+maps an I/O DMA address to a physical memory address). However, to be
portable, device driver writers may *not* assume that such an IOMMU
exists.
dma_map_sg(struct device *dev, struct scatterlist *sg,
int nents, enum dma_data_direction direction)
-Returns: the number of bus address segments mapped (this may be shorter
+Returns: the number of DMA address segments mapped (this may be shorter
than <nents> passed in if some elements of the scatter/gather list are
physically or virtually adjacent and an IOMMU maps them with a single
entry).
API.
Note: <nents> must be the number you passed in, *not* the number of
-bus address entries returned.
+DMA address entries returned.
void
dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
phys_addr is the CPU physical address to which the memory is currently
assigned (this will be ioremapped so the CPU can access the region).
-device_addr is the bus address the device needs to be programmed
+device_addr is the DMA address the device needs to be programmed
with to actually address this memory (this will be handed out as the
dma_addr_t in dma_alloc_coherent()).
projects / cascardo / linux.git / blobdiff