Re: IDE?

[Anton Altaparmakov]

At 19:16 17/08/02, Jan-Benedict Glaw wrote:
>On Fri, 2002-08-16 18:35:29 -0700, Linus Torvalds <[e-mail]>
>wrote in message <[e-mail]>:
> > On Fri, 16 Aug 2002, Alexander Viro wrote:
>
> >     - in particular, it would only bother with PCI (or better)
> >       controllers, and with UDMA-only setups.
>[...]
> > And then in five years, in Linux-3.2, we might finally just drop support
> > for the old IDE code with PIO etc. Inevitably some people will still use
>
>That's bad. Then, you're nailed to use old kernels without having
>possibilities of recent kernels only because you're working with eg. old
>Alphas, PCMCIA-IDE things or so? Bad, bad, badhorribly bad. Even it's
>sloooow, there'll always some need for PIO-only controller support...

I don't think it is possible to have DMA only drivers. On DMA 
failure/timeouts/whatever, the current DMA drivers always fall back to PIO 
mode and this is a good thing. Otherwise many transfers would simply fail. 
Dropping PIO mode fallback would mean a lot of IO errors. Any system put 
under stress will at some point fall back to PIO mode (at least judgjing 
from the limited number of systems I have) because it doesn't manage to do 
the DMA transfers in time. That was very visible during the period when 
Andre's new IDE core went into 2.5.something_early and it turned out that 
PIO was broken at that point. For example my VIA box was running just fine 
then in DMA mode but as soon as I put it under stress it blew up due to it 
falling out of DMA and the then broken PIO mode... And VIA686b is 
mainstream hardware...

Best regards,

         Anton