Re: WD_QUIRK_FORCE_LBA48

[Christoph Badura <bad%bsd.de@localhost>]

On Tue, Dec 15, 2009 at 10:35:37AM +0100, Manuel Bouyer wrote:
> ATA up to and including ATA6 says that words 60-61 shall be less than
> or equal to 0x10000000. ATA7 made this 0xfffffff (no idea why)
> which means that the last sector effectively addressable by LBA28
> effectively decreased by one sector between ATA6 and ATA7.

Yes, however, the sector 0xfffffff is accessible via LBA48 on drives that
support LBA48.

The check I proposed in the patch effectively is:

if (drive supports LBA48) {
        if (transfer accesses sectors beyond 0xffffffe)
                use LBA48 transfer;
}
else
        use LBA28 transfer;

So, for non-LBA48 drives all 2^28 sectors are accessible in LBA28 mode.
But for LBA48 drives only 2^28-1 in LBA28 mode and the rest in LBA48 mode.

All the version of the ATA-5/6 specs I looked at demand that a drive
fail a transfer that goes beyond the last user accessible sector as reported
in word 60:61 in LBA28 mode.  Hence we can't rely on accessing that last
sector when only LBA28 mode is feasible and the drive reports the limit
as 0xfffffff.

> I just figured that the best way to handle this is probably to use
> the content of words 60-61 as the LBA48 boundary then.

I think that is unecessary.  Because in sectors 0 to 0xffffffe are accessible
in LBA48 mode, too.  It is only important to use LBA48 commands for the
sectors above the boundary.  But below the boundary LBA48 and LBA28 both
will work.

--chris