]> err.no Git - linux-2.6/commit
[PATCH] dma doc updates
authorDavid Brownell <david-b@pacbell.net>
Sat, 1 Apr 2006 18:21:52 +0000 (10:21 -0800)
committerGreg Kroah-Hartman <gregkh@suse.de>
Fri, 14 Apr 2006 19:25:26 +0000 (12:25 -0700)
commit21440d313358043b0ce5e43b00ff3c9b35a8616c
tree32f3ed659a76ad6e4a6061b57346178cf3fa6256
parent2d1e1c754d641bb8a32f0ce909dcff32906830ef
[PATCH] dma doc updates

This updates the DMA API documentation to address a few issues:

 - The dma_map_sg() call results are used like pci_map_sg() results:
   using sg_dma_address() and sg_dma_len().  That's not wholly obvious
   to folk reading _only_ the "new" DMA-API.txt writeup.

 - Buffers allocated by dma_alloc_coherent() may not be completely
   free of coherency concerns ... some CPUs also have write buffers
   that may need to be flushed.

 - Cacheline coherence issues are now mentioned as being among issues
   which affect dma buffers, and complicate/prevent using of static and
   (especially) stack based buffers with the DMA calls.

I don't think many drivers currently need to worry about flushing write
buffers, but I did hit it with one SOC using external SDRAM for DMA
descriptors:  without explicit writebuffer flushing, the on-chip DMA
controller accessed descriptors before the CPU completed the writes.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Documentation/DMA-API.txt
Documentation/DMA-mapping.txt