He only has the one device on IDE as you can see that the probe only shows 
hdb, and i have a PIIX4 too and they do UDMA33 well enough, in fact i'm not 
aware of any DMA problems with the PIIX4. Richard, have you tried disabling 
CONFIG_IDEDMA_AUTO and CONFIG_PIIX_TUNING ?
But looking at the code in ide-features.c it doesn't look like we have 
enabled DMA by the time we get to that code.
     if (error) {
                (void) ide_dump_status(drive, "set_drive_speed_status", stat);
                return error;
        }
<----- snip ----- >
#if defined(CONFIG_BLK_DEV_IDEDMA) && !defined(CONFIG_DMA_NONPCI)
        if (speed > XFER_PIO_4) {
                outb(inb(hwif->dma_base+2)|(1<<(5+unit)), hwif->dma_base+2);  
      } else {
                outb(inb(hwif->dma_base+2) & ~(1<<(5+unit)), 
hwif->dma_base+2);
        }
#endif /* (CONFIG_BLK_DEV_IDEDMA) && !(CONFIG_DMA_NONPCI) */
But bear in mind i'm far from being remotely knowledgeable about this 
specific code ;)
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