On Mon, Jan 04, 2010 at 05:39:58PM +0000, Alan Cox wrote:
> > Firstly, icside shares its two IDE channels with one DMA engine - so it's
> > a simplex interface. IDE supports those (or did when the code was written)
> > serializing requests between the two interfaces. libata does not.
>
> Libata does the driver may not.
libata certainly didn't when I wrote the driver in 2007.
int ata_do_set_mode(struct ata_link *link, struct ata_device **r_failed_dev)
{
/* Record simplex status. If we selected DMA then the other
* host channels are not permitted to do so.
*/
if (used_dma && (ap->host->flags & ATA_HOST_SIMPLEX))
ap->host->simplex_claimed = ap;
...
static void ata_dev_xfermask(struct ata_device *dev)
{
...
if ((host->flags & ATA_HOST_SIMPLEX) &&
host->simplex_claimed && host->simplex_claimed != ap) {
xfer_mask &= ~(ATA_MASK_MWDMA | ATA_MASK_UDMA);
ata_dev_printk(dev, KERN_WARNING, "simplex DMA is claimed by "
"other device, disabling DMA\n");
}
and apparantly still doesn't. Only one channel of a simplex device is
permitted to be configured for DMA at any one time.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of:
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