Re: [PATCH v6 3/6] ata: libata-scsi: route non-zero LUN commands for multi-LUN ATAPI

[Hannes Reinecke]

On 6/8/26 23:34, 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.  Hoist a non-zero LUN early-exit ahead of the original
>     channel/id checks: when scsidev->lun is non-zero, allow it through
>     only if the underlying ata_device is ATAPI class.  The original
>     LUN-0 path is left structurally unchanged.
>
> 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.
>
>     The SCSI layer caps the LUN at shost->max_lun, so a value beyond
>     the device's nr_luns should never reach this point; guard with
>     WARN_ON_ONCE() and return AC_ERR_INVALID if it does, since the
>     3-bit CDB field cannot represent it.
>
> Signed-off-by: Phil Pemberton <philpem@xxxxxxxxxxxxx>
> ---
>   drivers/ata/libata-scsi.c | 32 ++++++++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
Reviewed-by: Hannes Reinecke <hare@xxxxxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
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