Re: use_10_for_ms revisited?

[Jeff Garzik <jgarzik@pobox.com>]

Matthew Dharm wrote:
> On Sun, Jun 29, 2003 at 02:30:28AM -0400, Jeff Garzik wrote:
> 
>>I was reading the specs just now, and I see that the inquiry page 
>>defines how ATAPI and USB devices indicate they are compliant with MMC-4.
> 
> 
> It does?  I guess I've missed that.

I'm looking at MMC-4 revision 2a (whatever was on t10.org tonight).

Immediately after table 286 (standard inquiry data format), it describes 
the information I believe we can use to determine that 10-byte commands 
(only) need to be sent.  peripheral qualifier, peripheral device type, 
version, and interface dependent field #1.

These fields can be used to differentiate atapi/usb devices from older 
scsi devices.  One concrete example is that atapi reports zero in the 
version field, even though it's mmc-4 compliant.  But the Linux scsi 
stack treats that instead as the most ancient of ancient scsi devices :) 
  So, to counteract this, the ide-scsi module and other places will 
patch the inquiry page data to indicate a higher scsi revision.

Other examples are several places where 6-byte commands are converted 
into 10-byte commands.  The right answer is to simply know when to send 
10-byte commands in the first place, thus eliminating the need for any 
translation.


> If you're talking about the INQUIRY command, the data better be within the
> first 36 bytes, or it's likely to not actually be there.

Certainly.

	Jeff