On Wed, Jan 14, 2009 at 8:32 AM, Vineet Gupta <[email protected]> wrote:
> Hi,
>
> I've read dma mapping and dma-api kernel documentation as well as the
> DMA API change at http://lwn.net/Articles/75780/ which describes fork
> of dma_sync_* to dma_sync_*_for_cpu and dma_sync_*_for_device.
>
> It seems the names of API are self explanatory and direction parameter
> is not needed (except for handling BIDIRECTIONAL case).
> So for e.g. If software wants to access the dma buffer, post DMA, it
> will invoke dma_sync_single_for_cpu so that non-coherent arch can
> invalidate the corresponding cache lines. This implies FROM_DEVICE
> semantics. Does that mean dma_sync_single_for_cpu invoked with
> direction = TO_DEVICE should return error.
drivers/ieee1394/sbp2.c:
static int sbp2_create_command_orb(struct sbp2_lu *lu,
struct sbp2_command_info *cmd,
struct scsi_cmnd *SCpnt)
{
dma_sync_single_for_cpu(dmadev, cmd->command_orb_dma,
sizeof(struct sbp2_command_orb), DMA_TO_DEVICE);
???
> Corollary case is when dma_sync_single_for_device is invoked with
> direction = FROM_DEVICE, is tha error too (buggy driver).
>
> The architecture for which I'm implementing DMA coherency APIs has
> non-coherent DMA memory and logical-to-bus mapping / DMA bounce is not
> a issue.
>
> Thanks,
> Vineet
>
--
Regards,
Peter Teoh
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