[PATCH v3 3/7] ata: libata-scsi: route non-zero LUN commands for multi-LUN ATAPI

[Phil Pemberton <philpem@philpem.me.uk>]

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.  LUNs
   beyond 7 cannot be encoded in the 3-bit CDB field; reject them
   with AC_ERR_INVALID.

Signed-off-by: Phil Pemberton <philpem@philpem.me.uk>
---
 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..48c7d323d6f9 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 (3-bit field) */
+	if (scmd->device->lun >= 8)
+		return AC_ERR_INVALID;
+	qc->cdb[1] = (qc->cdb[1] & 0x1f) | ((u8)scmd->device->lun << 5);
+
 	qc->complete_fn = atapi_qc_complete;
 
 	qc->tf.flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE;
@@ -3059,19 +3064,27 @@ static struct ata_device *ata_find_dev(struct ata_port *ap, unsigned int devno)
 static struct ata_device *__ata_scsi_find_dev(struct ata_port *ap,
 					      const struct scsi_device *scsidev)
 {
+	struct ata_device *dev;
 	int devno;
 
 	/* skip commands not addressed to targets we simulate */
 	if (!sata_pmp_attached(ap)) {
-		if (unlikely(scsidev->channel || scsidev->lun))
+		if (unlikely(scsidev->channel))
 			return NULL;
 		devno = scsidev->id;
 	} else {
-		if (unlikely(scsidev->id || scsidev->lun))
+		if (unlikely(scsidev->id))
 			return NULL;
 		devno = scsidev->channel;
 	}
 
+	if (unlikely(scsidev->lun)) {
+		dev = ata_find_dev(ap, devno);
+		if (!dev || dev->class != ATA_DEV_ATAPI)
+			return NULL;
+		return dev;
+	}
+
 	return ata_find_dev(ap, devno);
 }
 
-- 
2.43.0