Re: WD_QUIRK_FORCE_LBA48

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

On Wed, Dec 16, 2009 at 12:25:28AM +0000, Jonathan A. Kollasch wrote:
> On Tue, Dec 15, 2009 at 10:24:32AM +0100, Manuel Bouyer wrote:
> > On Tue, Dec 15, 2009 at 08:26:15AM +0000, Michael van Elst wrote:
> > > bouyer%antioche.eu.org@localhost (Manuel Bouyer) writes:
> > > 
> > > >There are ATA-5 drives reporting LBA48 supports. LBA48 showed up before
> > > >ATA-6 was out (like much features in ATA world, in fact).
> > > 
> > > I think it is bogus to rely on ATA-5 specifics (LBA28 is up to 2^28)
> > > for devices that do not follow that standard by extending it.
> > > 
> > > Making the decision on the LBA48 capability is more likely to
> > > succeed. In particular, because this can only fail for a
> > > very rare condition and only for the last two sectors.
> > 
> > The fact that it's only for the last sector doesn't make the problem
> > less critical.
> 
> And the fact that wd(4) now hardlocks Chris's hardware isn't
> even more critical?
> 
> Drives that conform to ATA-6 and greater are going to continue
> to become more common.  Treating them as the exception is not
> a good idea.
> 
> People using drives larger than 2^28-1 sectors on LBA48-incompatible
> controllers are treading on thin ice to begin with.  Very many LBA48
> drives won't even let you access sector 2^28-1 using a LBA28 command.
> These drives conform to the current ATA standard.
> 
> I don't like what the standard now says either.  But we can't just
> ignore the current standard because we don't like what it says.
> 
> We probably aren't going to get any complaints if we require
> LBA48 commands to access sector 0xfffffff.  If we do get
> complaints, we would have the standard on our side.

What I propose is actually conform to the standards, even more than
what Chris proposes. The content of words (60-61) is the
last LBA28-accessible sector+1, whatever version of the spec.
Using this will work in all cases.

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