[PATCH] ata: libata-scsi: Use correct device no in ata_find_dev()

[Damien Le Moal <dlemoal@kernel.org>]

For non-pmp attached devices managed directly by libata, the device
number is always 0 or 1 and lower to the maximum number of devices
returned by ata_link_max_devices(). However, for libsas managed devices,
devices are numbered up to the number of device scanned on an HBA port,
while each device has a regular ata/link setup supporting at most 1
device per link. This results in ata_find_dev() always returning NULL
except for the first device with device number 0.

Fix this by rewriting ata_find_dev() to ignore the device number for
non-pmp attached devices with a link with at most 1 device. For these,
device number 0 is always used to return the correct ata_device struct
of the port link. This change excludes IDE master/slave setups (maximum
number of devices per link is 2) and port-multiplier attached devices.

Reported-by: Xingui Yang <yangxingui@huawei.com>
Fixes: 41bda9c98035 ("libata-link: update hotplug to handle PMP links")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
---
 drivers/ata/libata-scsi.c | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 7bb12deab70c..3ba9cb258394 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -2696,16 +2696,33 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc)
 
 static struct ata_device *ata_find_dev(struct ata_port *ap, int devno)
 {
-	if (!sata_pmp_attached(ap)) {
-		if (likely(devno >= 0 &&
-			   devno < ata_link_max_devices(&ap->link)))
+	if (unlikely(devno < 0))
+		return NULL;
+
+	if (likely(!sata_pmp_attached(ap))) {
+		/*
+		 * For the non PMP case, the maximum number of devices per link
+		 * is 1 (e.g. SATA case), or 2 (IDE master + slave). The former
+		 * case includes libsas hosted devices which are numbered up to
+		 * the number of devices scanned on an HBA port, but with each
+		 * ata device having its own ata port and link. To accommodate
+		 * these, ignore devno and always use device number 0.
+		 */
+		switch (ata_link_max_devices(&ap->link)) {
+		case 1:
+			return &ap->link.device[0];
+		case 2:
+			if (devno >= 2)
+				return NULL;
 			return &ap->link.device[devno];
-	} else {
-		if (likely(devno >= 0 &&
-			   devno < ap->nr_pmp_links))
-			return &ap->pmp_link[devno].device[0];
+		default:
+			return NULL;
+		}
 	}
 
+	if (devno < ap->nr_pmp_links)
+		return &ap->pmp_link[devno].device[0];
+
 	return NULL;
 }
 
-- 
2.40.1