Re: [PATCH] libata: fix ATA passthrough handling for ATAPI devices

[Jeff Garzik <jgarzik@pobox.com>]

Tejun Heo wrote:
> libata used to pass all SCSI commands directly to ATAPI devices.
> However, this is incorrect for ATA passthrough commands as they must
> be handled by the SAT layer in libata.  Also, regardless of the
> attached ATAPI device's supported packet length, SAT says that both
> flavors of passthrough commands (ATA12 and ATA16) should work.
> 
> This patch makes the following changes to fix ATA passthrough handling
> for ATAPI devices.
> 
> * implement atapi_get_xlat_func() and make libata handle ATA12 and
>   ATA16 in SAT layer instead of passing it directly to the target
>   device even if the device is ATAPI.
> 
> * Always allow 16byte CDBs for ATAPI devices.  This makes

This is definitely wrong.  Some ATAPI devices are limited to 12-byte CDBs.

Also, are we sure that no ATAPI device ever implements these opcodes?

Prior to the SAT spec -- which includes most ATAPI firmwares -- those 
opcodes might have been vendor-reserved space.  Did you or Doug verify 
against the older specifications who might care about these opcodes?

Or maybe there is a flag somewhere we can abuse, that permits support of 
both scenarios -- passing the command to the device, and handling the 
command internally?

	Jeff