Consistent memory is memory for which a write by either the device or
the processor can immediately be read by the processor or device
-without having to worry about caching effects. (You may however need
-to make sure to flush the processor's write buffers before telling
-devices to read that memory.)
+without having to worry about caching effects.
This routine allocates a region of <size> bytes of consistent memory.
it also returns a <dma_handle> which may be cast to an unsigned
could not be created and the driver should take appropriate action (eg
reduce current DMA mapping usage or delay and try again later).
- int
- dma_map_sg(struct device *dev, struct scatterlist *sg,
- int nents, enum dma_data_direction direction)
- int
- pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg,
- int nents, int direction)
+int
+dma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
+ enum dma_data_direction direction)
+int
+pci_map_sg(struct pci_dev *hwdev, struct scatterlist *sg,
+ int nents, int direction)
Maps a scatter gather list from the block layer.
aborting the request or even oopsing is better than doing nothing and
corrupting the filesystem.
-With scatterlists, you use the resulting mapping like this:
-
- int i, count = dma_map_sg(dev, sglist, nents, direction);
- struct scatterlist *sg;
-
- for (i = 0, sg = sglist; i < count; i++, sg++) {
- hw_address[i] = sg_dma_address(sg);
- hw_len[i] = sg_dma_len(sg);
- }
-
-where nents is the number of entries in the sglist.
-
-The implementation is free to merge several consecutive sglist entries
-into one (e.g. with an IOMMU, or if several pages just happen to be
-physically contiguous) and returns the actual number of sg entries it
-mapped them to. On failure 0, is returned.
-
-Then you should loop count times (note: this can be less than nents times)
-and use sg_dma_address() and sg_dma_len() macros where you previously
-accessed sg->address and sg->length as shown above.
-
- void
- dma_unmap_sg(struct device *dev, struct scatterlist *sg,
- int nhwentries, enum dma_data_direction direction)
- void
- pci_unmap_sg(struct pci_dev *hwdev, struct scatterlist *sg,
- int nents, int direction)
+void
+dma_unmap_sg(struct device *dev, struct scatterlist *sg, int nhwentries,
+ enum dma_data_direction direction)
+void
+pci_unmap_sg(struct pci_dev *hwdev, struct scatterlist *sg,
+ int nents, int direction)
unmap the previously mapped scatter/gather list. All the parameters
must be the same as those and passed in to the scatter/gather mapping