Re: 2.6.32: Promise UDMA33 card refuses to work in UDMA mode

[Russell King <rmk@arm.linux.org.uk>]

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: