Re: Request for help to identify some bugs (part two)
On Sun, 2005-10-23 at 09:59 +1000, Dean Hamstead wrote:
> >>In fact, setting it to udma2 makes it no longer work, does the kernel is
> >>"aware" of this limitation and sets mdma2 as a consequence?
> >
> >
> > How do you set it to u/dma2 and remind me the exact machine model
>
> cdroms dont support dma?? i thought they were pio only
>
> with every cdrom on any arch when iveset to dma its
> been time for bus errors. pio is fine though. like
> i said, im 99% sure this is a limitation of cdroms.
> linked to how cdroms shouldnt be the master device
> with a slave hard disk.
Nahhhh :) PIO would be really bad, especially with those modern fast
readers :)
In fact, most really recent CD drives can do U/DMA2 or even more.
The macs however have this wired in various ways, depending on the
machine model, the drive may sit on a MDMA bus only, also some early CD
drives that claimed to do U/DMA wouldn't do it very reliably.
Also, when changing the DMA speed, it's important that it's done
properly (that is the right command is sent ot the drive at the right
time while the host controller reconfigures its own speed).
I'm not 100% sure what hdparm vs. kernel ide driver do when using hdparm
-X here (do they only send the command to the disk or do they properly
deal with the host controller setting as well).
Normally, the kernel powermac IDE driver should default to the optimal
setting for the drive.
Ben.
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