Re: [Patch] dma_sync_to_device

["David S. Miller" <davem@redhat.com>]

On Wed, 11 Feb 2004 09:39:01 -0700
Deepak Saxena <dsaxena@plexity.net> wrote:

> If pci_dma_sync_single is for FROM_DEVICE only, than the direction
> parameter should go away from it and the from
> pci_dma_sync_to_device_single().

This is wrong.  The direction parameter says what was done by the device/cpu
for the DMA, this is needed by the port to know how to perform the
pci_dma_sync_single et al. correctly.

For example, a port may have to do something different for FROM_DEVICE vs.
TO_DEVICE to properly execute the pci_dma_sync_single() request.

MIPS (and seemingly ARM) are probably the best platforms by which to draw up
the worst case scenerio for the implementation of these things :) and thus
the optimizations made possible by certain combinations of request+direction.