Re: Streaming DMA mapping question

[David S. Miller]

   From: Adam Kropelin <[e-mail]>
   Date: Fri, 13 Sep 2002 15:39:16 -0400
   
   According to the docs, you should either unmap or sync your DMA buffer before
   touching it from the host. The i386 implementation of pci_unmap is empty --no
   problem; there must not be any unmap work to do on this arch. But the 
   implementation of pci_dma_sync does contain a flush_write_buffers() call. This
   makes me think that perhaps if I'm going to modify the buffer before I submit it
   back to the controller I need to do:

Actually, rather it appears that the i386 pci_unmap_*() routines need
the write buffer flush as well.

The x86 implementation is a bad example to read if you're trying to
see what the worst case scenerio is.

Just follow the document and your driver will work properly on all
platforms.  DMA-mapping.txt was meant to be written in a way such
that you should not ever need to look at an implementation of the
interfaces to figure out how to use them.