Re: [CFT] Bus mastering support for IDE CDROM audio

[Ed Sweetman <ed.sweetman@wmich.edu>]

I've always been able to get it back to dma for packet by forcing the
drive to sleep mode and then letting the kernel wake it.   I guess I'll
try this 3rd version patch when I get back from class today and see if
that still works.   

hdparm -Y /dev/cdrom    

then go and set dma again with hdparm.   

Although this could just be fickleness of my cdrom.  


On Mon, 2002-01-28 at 04:51, Andrew Morton wrote:
> benh@kernel.crashing.org wrote:
> > 
> > >At no stage does a packet-mode DMA error turn off drive-level
> > >DMA.  This is because some devices seem to perform ordinary
> > >ATA DMA OK, but screw up packet DMA.
> > >
> > >The kernel internally retries the requests when it performs fallback,
> > >so userspace shouldn't see any disruption as the kernel works
> > >out what to do.
> > >
> > >Once the drive has fallen back to single-frame (or PIO mode) for
> > >packet reads, the only way to get it back to a higher level is
> > >a reboot.
> > 
> > Doesn that mean that a bad media (typically a scratched CDROM) will
> > cause the drive to revert to PIO until next reboot ?
> > 
> 
> Nope.  This error handling is specifically for busmastering
> errors, not for media errors.
> 
> I've tested media errors (whiteboard marker scribblings on the
> CD do this nicely).  DMA errors (bad return value from
> HWIF->dmaproc) I can only simulate.
> 
> 
> -