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

[Mark Lord <liml@rtr.ca>]

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.

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.

Cheers