libata vs ATAPI

[Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>]

Hi Jeff,

Is libata currently supposed to work with ATAPI
(I know about lack of REQUEST_SENSE support)?

With ATA_ENABLE_ATAPI defined INQUIRY seems to succeed for my
TOSHIBA ODD-DVD SD-R6372 but empty info is printed by SCSI layer.

Then REPORT_LUNS errors out (dev_stat = 0x51)...

I've noticed that DMA is used by default for all packet commands
which doesn't seem to be wise thing to do so I disabled it.
Unfortunately it doesn't help because atapi_pio_sector() assumes
transfer length to be % SECTOR_SIZE and transfer length for INQUIRY
is mere 36 bytes so this fails.

This comment in atapi_pio_sector():

	/* make sure byte count is multiple of sector size; not
	* required by standard (warning! warning!), but IDE driver
	* does this to simplify things a bit.  We are lazy, and
	* follow suit.
	*/
	if (bytes & (ATA_SECT_SIZE - 1))
		goto err_out;

looks very suspicious because ide-cd and ide-scsi seem
to be doing this but only for READ/WRITE commands.

Also ATAPI-SCSI emulation is still missing in libata-scsi.c.

I'm sure you know more about what needs to be done.
Could you make some nice, detailed TODO? :-)

Thanks,
Bartlomiej