Re: drvctl rescan for atabus

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Oct 09, 2009 at 04:58:43PM -0500, David Young wrote:
> > there's another reason to do request all devices to be detached before
> > rescan: in ATA the master and slave devices are probed at the same
> > time, they can't really be probed independantly ...
> > This probably could be fixed by doing the probe without attach, but this
> > adds complexity to the driver (you have to stall I/Os while doing
> > this) and I'm not sure it's worth it. 
> 
> I think that if the devices are hotpluggable, then it is definitely
> worth it to attach/detach the disks independently.  Think of four SATA
> ports, each attached to a disk in a RAID5 configuration.  (Perhaps the
> code under discussion will not be involved in SATA hotplug?)

I think it's hard to do SATA hotplug properly without access to
the SATA registers. With SATA registers we can do the probe in
a different way (the SATA registers will tell us if there's a
device or not).

> 
> If the devices are not hotpluggable, however, it is not necessary to
> re-probe, is it?  We can use the last probe results, which should not
> have changed since boot.  Maybe I am mistaken about that.

Unfortunably some are really hot-plug, think media bay on some laptop.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--