Re: A note on libata passthru patch

["John W. Linville" <linville@tuxdriver.com>]

On Sun, Aug 21, 2005 at 05:37:18PM -0400, Jeff Garzik wrote:
> 
> Something that Alan unintentionally reminded me, about the libata 
> passthru patch:  Some controllers require certain ATA commands to be 
> synchronized at the host-wide level.

<snip>

> Currently probing is 100% synchronous, so our internal use of SET 
> FEATURES - XFER MODE is safe.  But when you turn on ATA passthru, it is 
> not safe.

...except that the passthru code specifically filters-out the SET
FEATURES - XFER MODE command. (libata_scsi.c:1976)
 
> This is another issue that needs fixing before we can merge the ATA 
> passthru feature, since the consequences can be serious.

I am by no means an expert either on ATA in general or on the oddities
and quirks of specific SATA controllers.  I don't know if anyone else
interested in the fate of the passthru patch is such an expert or not,
but either way it would likely be helpful to list any other specific
synchronization issues known to date which might be problematic.

Presuming that such a list either exists or is likely to exist, does
anyone have suggestions for what needs to be done in the general
case here?  Perhaps some infrastructure needs to be added to verify
that it is okay for the passthru stuff to issue a given command at a
given time on a given controller?  Sounds complicated...  Maybe some
infrastructure to quiesce _everything_ on the controller before
issuing a passthru command?  Just thinking "out loud"...

I'd like to help (and I'd like the passthru stuff to be "in"), but
I need some guidance...

John
-- 
John W. Linville
linville@tuxdriver.com