On Tue, 2007-01-02 at 19:35 -0500, Mark Lord wrote: > In an ideal world, we would use the existing ATA_12 opcode > to issue 12-byte ATA passthrough commands for libata ATAPI drives > from userspace. > > But ATA_12 happens to have the same SCSI opcode value as the older > CD/RW "BLANK" command, widely used by cdrecord and friends. It's not older; it's still current (at least as of MMC-5) > So, to achieve ATA passthru capability for libata ATAPI, > we have to instead use the ATA_16 opcode: a 16-byte command. > > SCSI normally disallows issuing 16-byte commands to 12-byte devices, > so special support has to be added for this. > > Introduce an "allow_ata_16" boolean to the scsi_host struct. > This provides a means for libata to signal that 16-byte ATA_16 > commands should be permitted even for 12-byte ATAPI devices. 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. You can see this in libata-scsi.c:__ata_scsi_queuecommand() where commands for ATAPI devices go globally through atapi_xlat(). So at the moment libata would send ATA_12 or ATA_16 over to an ATAPI device also as an ATA PACKET command. Is there a missing piece to this patch, where you scan the incoming commands to ATAPI devices and actually do translation for ATA_16? James - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
