Re: [PATCH 1/1] ide: Allow disabling of UDMA for Compact Flash devices

["James Ausmus" <james.ausmus@gmail.com>]

On 4/18/06, Robert Hancock <hancockr@shaw.ca> wrote:
> James Ausmus wrote:
> > This is exactly the situation that I have with 2 separate "dumb" (just
> > physical interfaces, essentially - not at all detectable) IDE->CF
> > adapters - both the IDE controller and the CF media support several
> > UDMA modes, so the IDE driver throws the CF device into UDMA mode on
> > bootup. However, as the physical interface between the IDE cable and
> > the CF socket is poorly engineered, it cannot handle the higher
> > speeds, causing the timeout errors. For some people, this can just be
> > fixed with an ide=nodma boot option, but as I also have a (quite
> > large) rotating media device on the controller, this is not an option,
> > as, if a fsck is performed on a boot, the boot-up time is upwards of
> > 30 minutes.
>
> If it's like some of the CF-IDE adapters I've seen, the DMA request/ack
> lines likely aren't even wired up between the card and the cable.
> There's no way the kernel can detect that DMA is not actually possible
> on such a card without trying and waiting for it to timeout. (I've seen
> a few which have jumpers which select whether to connect these or not -
> haven't a clue why you wouldn't want to hook those up unconditionally..)
>
> Isn't there an option to disable DMA for a specific IDE channel
> (ide2=nodma or something like that)?
>

Yes, there is, but that unfortunately does not solve the issue for
configurations where there is also a UDMA capable device on the same
channel. If there was something like ide2=0:nodma,1:dma or some such,
in order to enable/disable dma on a per device basis, instead of a
per-channel basis, then that would also solve the issue.

-James


> --
> Robert Hancock      Saskatoon, SK, Canada
> To email, remove "nospam" from hancockr@nospamshaw.ca
> Home Page: http://www.roberthancock.com/
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