Re: [PATCH v2 3/5] ata: libata-scsi: route non-zero LUN commands for multi-LUN ATAPI

[Phil Pemberton]

On 23/04/2026 12:08, Hannes Reinecke wrote:
> On 4/20/26 14:23, Phil Pemberton wrote:
> > Two changes are required to route commands to ATAPI LUNs other than 0:
> >
> > 1. __ata_scsi_find_dev():  The existing code rejects any scsi_device
> >     with a non-zero LUN, returning NULL and dropping the command on
> >     the floor.  Relax both the PMP and non-PMP branches to allow
> >     non-zero LUNs through when the underlying ata_device is ATAPI
> >     class, since ATAPI devices can legitimately expose multiple LUNs.
> >
> > 2. atapi_xlat():  Older ATAPI devices (SCSI-2 era) expect the LUN in
> >     CDB byte 1 bits 7:5 rather than relying on transport-level LUN
> >     addressing.  Encode scmd->device->lun into those bits, preserving
> >     the existing command-specific bits in 4:0.  This is required by
> >     both the Panasonic PD/CD combos and Nakamichi CD changers.
> >
> > Signed-off-by: Phil Pemberton <philpem@xxxxxxxxxxxxx>
> > ---
> >   drivers/ata/libata-scsi.c | 17 +++++++++++++++--
> >   1 file changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> > index 317883bac25f..4e88ae7d94c3 100644
> > --- a/drivers/ata/libata-scsi.c
> > +++ b/drivers/ata/libata-scsi.c
> > @@ -2951,6 +2951,11 @@ static unsigned int atapi_xlat(struct 
> > ata_queued_cmd *qc)
> >       memset(qc->cdb, 0, dev->cdb_len);
> >       memcpy(qc->cdb, scmd->cmnd, scmd->cmd_len);
> > +    /* SCSI-2 CDB LUN encoding: bits 7:5 of byte 1 */
> > +    if (scmd->device->lun < 8)
> > +        qc->cdb[1] = (qc->cdb[1] & 0x1f) |
> > +                  ((u8)scmd->device->lun << 5);
> > +
>
> Hmm. And what happens when scmd->device->lun is _greater_ than 7?
> We surely should abort that command, shouldn't we?

I was about to say "you can't have LUNs greater than seven" until I saw 
it's been extended in later versions of the standard.

What's the preferred way to abort the command in this context?

--
Phil.
philpem@xxxxxxxxxxxxx
https://www.philpem.me.uk/