Re: [PATCH] SCSI, libata: add support for ATA_16 commands to libata ATAPI devices

[Jeff Garzik <jeff@garzik.org>]

James Bottomley wrote:
> On Wed, 2007-01-03 at 00:42 -0500, Mark Lord wrote:
>> James Bottomley wrote:
>>> I don't think I quite understand what you're trying to do here.  My
>>> understanding is that ATA_12 and ATA_16 are part of the SAT layer. i.e.
>>> they're used when we're speaking SCSI to an underlying ATA device to
>>> send taskfiles.  However, ATAPI devices don't use SAT ... every SCSI
>>> command you send to an ATAPI device goes out as an ATA PACKET command
>>> without being translated.
>> ATAPI devices also implement quite a few ATA (non-packet) commands.
>> This patch gives us a way to issue them in response to SG_IO ATA passthru
>> and the existing (non working) libata HDIO_DRIVE_CMD and HDIO_DRIVE_TASK
>> ioctl calls.
> 
> I know that ... but when you send ATA_16 down to an ATAPI device via
> SG_IO  the code paths in libata don't unwrap it and send it out as a
> taskfile ... they put ATA_16 out as a packet command.

He is aware of that.  That's what his two patches address.


>> Without this patch, SCSI blocks the ATA_16 passthru attempts,
>> because it thinks the CDB is too large for the 12-byte packet protocol
>> that ATAPI devices use.  This limit (12 bytes) is totally non-applicable
>> to ATA protocol commands.
>>
>>> Is there a missing piece to this patch, where you scan the incoming
>>> commands to ATAPI devices and actually do translation for ATA_16?
>> Look at the existing libata-core.c ioctl's for HDIO_DRIVE_CMD
>> and HDIO_DRIVE_TASK, used by hdparm and others.
> 
> Those send out taskfile commands ... my point is that the SAT SCSI

No, those HDIO_xxx ioctls cause libata to send ATA_{12,16} SCSI commands 
to the SCSI simulator (which then unwraps them, and sends a taskfile).

	Jeff