Re: ata(4) and NCQ

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

On Tue, 26 Apr 2011, Manuel Bouyer wrote:

> Actually I suspect the idea to have ATA drives show up as SCSI comes from
> windows. But this was done so on windows because of a limitation of the
> windows kernel: if you want to have a drive appears as ATA the controller
> has to follow the pciide 1 specification. if you have a smarter controller,
> the only way to have full control at the controller driver level is to
> register it as a SCSI driver.

I can speak to this.  (I probably shouldn't, but that's never stopped me 
before.)  Solaris has this problem where making even a tiny a code change 
involves huge amounts of overhead.  What typically happened is a bug is 
found on a SCSI disk, which is fixed.  Then the same problem occurs on a 
CDROM, ATA disk, etc.  Having one driver handle all devices solves this 
problem so when something is fixed for SCSI disks it applies to 
fibre-channel disks, CDROMs, etc.  Of course, this causes other problems 
like complicating the sd driver much more than it would have to be to only 
support SCSI disks instead of also CDROMs, removable devices, 
fibre-channel disks, SAS disks, SATA disks, etc.

Eduardo