Re: [SCSI] Add support for braindead Cypress USB ATA passthrough CDBs

[James Bottomley <James.Bottomley@SteelEye.com>]

On Wed, 2005-12-21 at 04:24 -0800, David Caldwell wrote:
> This patch does 2 things. It reimplements the SG_FLAG_LUN_INHIBIT flag
> in the SG_IO ioctl which stops the scsi subsystem from overwriting the
> 2nd byte of the CDB with the LUN. It also doesn't guess the CDB length
> when sending the SG_IO ioctl to the sg device (the main scsi_ioctl
> already did this).
> 
> This is for the Cypress CY7C68310 USB to ATA bridge chip (and most
> likely other USB to ATA chips from Cypress), which implements an ATA
> passthrough command that is 16 bytes long and starts with the bytes
> 0x24 0x24. (Not vendor unique, weird length for opcode 0x24, and
> misuse of the LUN area all at the same time--Lovely).

I think this approach is too invasive to the stack.  When this was
discussed in november, there wasn't much enthusiasm for resurrecting the
long dead LUN_INHIBIT flag.  The two suggested mechanisms are

1) Simply don't mangle the LUN for SCSI_UNKNOWN and then have all the
subsystems lying about SCSI_2 compliance instead set their mangled level
to SCSI_UNKNOWN (which seems to be more truthful)

2) If 1) doesn't work, then use a blacklist entry which the subsystems
would also have access to.

James