[PATCH 3/3] ata: libata-scsi: probe additional LUNs for multi-LUN ATAPI devices

[Phil Pemberton]

Some ATAPI devices (e.g. the Panasonic PD/CD combo drives) implement
multiple logical units. For instance the aforementioned PD/CD has a CD
drive on LUN 0 and the rewritable Phase-change Dual (PD) block device on
LUN 1.

ata_scsi_scan_host() previously only scanned LUN 0 via
__scsi_add_device(). With the multi-LUN work now in place, extend this
scan to probe for additional LUNs on devices which have BLIST_FORCELUN
set in the SCSI device info table.

Scanning stops when __scsi_add_device() fails, or the device reports
device type 0x1f (unknown or no device type). The PD drive returns this
for unimplemented LUNs.

The aforementioned BLIST_FORCELUN guard prevents non-multilun devices
from being affected.

Tested with a Panasonic LF-1195C PD/CD with Compaq firmware, which now
correctly enumerates as a CD drive (sr) and PD optical drive (sd).

Also tested with a LITE-ON iHAS124 DVD drive, which has a single LUN and
ignores the LUN parameter in the CDB. As a result, without the
BLIST_FORCELUN guard, this drive would pop up as eight separate devices.

Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Phil Pemberton <philpem@xxxxxxxxxxxxx>
---
 drivers/ata/libata-scsi.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index dc6829e60fb3..0a7ce44118fe 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -4732,6 +4732,35 @@ void ata_scsi_scan_host(struct ata_port *ap, int sync)
 			if (!IS_ERR(sdev)) {
 				dev->sdev = sdev;
 				ata_scsi_assign_ofnode(dev, ap);
+				/*
+				 * Multi-LUN ATAPI devices (e.g. PD/CD combo
+				 * drives) are flagged BLIST_FORCELUN in
+				 * scsi_devinfo.  Probe additional LUNs when
+				 * the flag is set.
+				 */
+				if (dev->class == ATA_DEV_ATAPI &&
+				    (sdev->sdev_bflags & BLIST_FORCELUN)) {
+					u64 lun;
+
+					for (lun = 1; lun < ap->scsi_host->max_lun;
+					     lun++) {
+						struct scsi_device *extra;
+
+						extra = __scsi_add_device(
+							ap->scsi_host,
+							channel, id, lun,
+							NULL);
+						if (IS_ERR(extra))
+							break;
+						/* PDT 0x1f: no device type */
+						if (extra->type == 0x1f) {
+							scsi_remove_device(extra);
+							scsi_device_put(extra);
+							break;
+						}
+						scsi_device_put(extra);
+					}
+				}
 				scsi_device_put(sdev);
 			} else {
 				dev->sdev = NULL;
-- 
2.39.5