Re: serialize access to ide device

[Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl>]

On Monday 02 August 2004 15:11, Jens Axboe wrote:
> Hi Bart,

Hi,

Late reply follows...

> 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.

> 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.

Bartlomiej