Merge git://git.kernel.org/pub/scm/linux/kernel/git/sam/kbuild

[linux-2.6-omap-h63xx.git] / Documentation / DMA-API.txt

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index 1af0f2d5022066f1a205ad5265771e3ab112c018..2ffb0d62f0fe3ed8156586505b7faf1efe1c33ce 100644 (file)
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -33,7 +33,9 @@ pci_alloc_consistent(struct pci_dev *dev, size_t size,
 
 Consistent memory is memory for which a write by either the device or
 the processor can immediately be read by the processor or device
 
 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.
+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.)

 
 This routine allocates a region of <size> bytes of consistent memory.
 it also returns a <dma_handle> which may be cast to an unsigned
 
 This routine allocates a region of <size> bytes of consistent memory.
 it also returns a <dma_handle> which may be cast to an unsigned


@@ -304,12 +306,12 @@ dma address with dma_mapping_error(). A non zero return value means the mapping
 could not be created and the driver should take appropriate action (eg
 reduce current DMA mapping usage or delay and try again later).
 
 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.
 
 
 Maps a scatter gather list from the block layer.
 


@@ -327,12 +329,33 @@ critical that the driver do something, in the case of a block driver
 aborting the request or even oopsing is better than doing nothing and
 corrupting the filesystem.
 
 aborting the request or even oopsing is better than doing nothing and
 corrupting the filesystem.
 

-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)
+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)

 
 unmap the previously mapped scatter/gather list.  All the parameters
 must be the same as those and passed in to the scatter/gather mapping
 
 unmap the previously mapped scatter/gather list.  All the parameters
 must be the same as those and passed in to the scatter/gather mapping