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List:       linux-kernel
Subject:    Re: serialize access to ide device
From:       Jens Axboe <axboe () suse ! de>
Date:       2004-08-21 10:32:09
Message-ID: 20040821103208.GF6755 () suse ! de
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On Thu, Aug 19 2004, Bartlomiej Zolnierkiewicz wrote:
> > 2.6 breaks really really easily if you have any traffic on a device and
> > issue a hdparm (or similar) command to it. Things like set_using_dma()
> > and ide_set_xfer_rate() just stomp all over the drive regardless of what
> > it's doing right now.
> 
> Yep, known problem.

Something should be done about it, it's pretty critical imho.

> > I hacked something up for the SUSE kernel to fix this _almost_, it still
> > doesn't handle cases where you want to serialize across more than a
> > single channel. Not a common case, but I think there is such hardware
> > out there (which?).
> >
> > Clearly something needs to be done about this, it's extremely
> > frustrating not to be able to reliably turn on dma on a drive at all.
> > I'm just tossing this one out there to solve 99% of the case, I'd like
> > some input from you on what you feel we should do.
> 
> What about adding new kind of REQ_SPECIAL request and converting 
> set_using_dma(), set_xfer_rate(), ..., to be callback functions for this 
> request?
> 
> This should be a lot cleaner and will cover 100% cases.

That will still only serialize per-channel. But yes, a lot cleaner.

-- 
Jens Axboe

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