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DMA-API.txt: add dma_sync_single/sg API description

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This adds the description of the following eight function:

dma_sync_single_for_cpu
pci_dma_sync_single_for_cpu
dma_sync_single_for_device
pci_dma_sync_single_for_device
dma_sync_sg_for_cpu
pci_dma_sync_sg_for_cpu
dma_sync_sg_for_device
pci_dma_sync_sg_for_device

It was unclear that the API permits a partial sync (some network drivers
already do though).  I made it clear that the sync_single API can do a
partial sync but the sync_sg API can't.

We could do a partial sync with the sync_sg API too, however, it's
difficult for driver writers to correctly use the sync_sg API for a
partial sync since the scatterlists passed in to the mapping API can't be
modified.  It's unlikely that driver writers want to do a partial sync
with the sync_sg API (because the sync_sg API are usually used for block
drivers).  So I think that it's better to forbid a partial sync with the
sync_sg API.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: David Miller <davem@davemloft.net>
Acked-by: James Bottomley <James.Bottomley@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
FUJITA Tomonori 2010-03-10 15:23:17 -08:00 committed by Linus Torvalds
parent 039956e919
commit 9705ef7ec8
1 changed files with 42 additions and 0 deletions
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42
Documentation/DMA-API.txt
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@ -364,6 +364,48 @@ API.
Note: <nents> must be the number you passed in, *not* the number of
physical entries returned.
void
dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
enum dma_data_direction direction)
void
pci_dma_sync_single_for_cpu(struct pci_dev *hwdev, dma_addr_t dma_handle,
size_t size, int direction)
void
dma_sync_single_for_device(struct device *dev, dma_addr_t dma_handle, size_t size,
enum dma_data_direction direction)
void
pci_dma_sync_single_for_device(struct pci_dev *hwdev, dma_addr_t dma_handle,
size_t size, int direction)
void
dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg, int nelems,
enum dma_data_direction direction)
void
pci_dma_sync_sg_for_cpu(struct pci_dev *hwdev, struct scatterlist *sg,
int nelems, int direction)
void
dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg, int nelems,
enum dma_data_direction direction)
void
pci_dma_sync_sg_for_device(struct pci_dev *hwdev, struct scatterlist *sg,
int nelems, int direction)
Synchronise a single contiguous or scatter/gather mapping for the cpu
and device. With the sync_sg API, all the parameters must be the same
as those passed into the single mapping API. With the sync_single API,
you can use dma_handle and size parameters that aren't identical to
those passed into the single mapping API to do a partial sync.
Notes: You must do this:
- Before reading values that have been written by DMA from the device
(use the DMA_FROM_DEVICE direction)
- After writing values that will be written to the device using DMA
(use the DMA_TO_DEVICE) direction
- before *and* after handing memory to the device if the memory is
DMA_BIDIRECTIONAL
See also dma_map_single().
dma_addr_t
dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size,
enum dma_data_direction dir,