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| author | James Bottomley <james.bottomley@steeleye.com> | 2004-06-29 05:20:29 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2004-06-29 05:20:29 -0700 |
| commit | 4ddc09038885e0906efea13e978be192147ef60f (patch) | |
| tree | e766bb8182f6aad6bb975f69e892c6bb54e30409 /Documentation | |
| parent | 55be71cfb77dc0a0a59716be3e1ac7946245ef67 (diff) | |
| download | history-4ddc09038885e0906efea13e978be192147ef60f.tar.gz | |
[PATCH] dma_get_required_mask()
This patch implements dma_get_required_mask() which may be used by drivers
to probe the optimal DMA descriptor type they should be implementing on the
platform.
I've also tested it this time with the sym_2 driver...making it chose the
correct descriptors for the platform. (although I don't have a 64 bit
platform with >4GB memory, so I only confirmed it selects the 32 bit
descriptors all the time...)
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/DMA-API.txt | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt index 2c1bd6a83fafc6..11caa2d64c013b 100644 --- a/Documentation/DMA-API.txt +++ b/Documentation/DMA-API.txt @@ -162,6 +162,20 @@ parameters if it is. Returns: 1 if successful and 0 if not +u64 +dma_get_required_mask(struct device *dev) + +After setting the mask with dma_set_mask(), this API returns the +actual mask (within that already set) that the platform actually +requires to operate efficiently. Usually this means the returned mask +is the minimum required to cover all of memory. Examining the +required mask gives drivers with variable descriptor sizes the +opportunity to use smaller descriptors as necessary. + +Requesting the required mask does not alter the current mask. If you +wish to take advantage of it, you should issue another dma_set_mask() +call to lower the mask again. + Part Id - Streaming DMA mappings -------------------------------- |