scsi: Revert "scsi: Fix sas_user_scan() to handle wildcard and multi-channel scans"

This reverts commit 37c4e72.

Said commit causes excessive resource usage and even system freeze with
some controllers, e.g. smartpqi and hisi_sas. The justification provided
by the patch authors [1] was supporting a special mode of the mpi3mr and
mpt3sas, so-called "Tri-mode", in which NVMe drives are exposed as SCSI
devices on a separate channel. While that's useful for these drivers, it
seems wrong to cause major breakage for other drivers for the sake of
this feature.

[1] https://lore.kernel.org/linux-scsi/CAFdVvOwjy+2ORJ6uJkspiLTPF05481U7gcS4QohFOFGPqAs8ig@mail.gmail.com/

Fixes: 37c4e72 ("scsi: Fix sas_user_scan() to handle wildcard and multi-channel scans")
Signed-off-by: Martin Wilck <martin.wilck@suse.com>
Cc: Don Brace <don.brace@microchip.com>
Cc: storagedev@microchip.com
Cc: Ranjan Kumar <ranjan.kumar@broadcom.com>
Cc: Sathya Prakash Veerichetty <sathya.prakash@broadcom.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumit Saxena <sumit.saxena@broadcom.com>
Cc: mpi3mr-linuxdrv.pdl@broadcom.com
Cc: MPT-FusionLinux.pdl@broadcom.com
Cc: Yihang Li <liyihang9@h-partners.c>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260513174236.430465-3-mwilck@suse.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Martin Wilck

drivers/scsi/scsi_scan.c

@@ -1921,7 +1921,7 @@ int scsi_scan_host_selected(struct Scsi_Host *shost, unsigned int channel,
 
 	return 0;
 }
-EXPORT_SYMBOL(scsi_scan_host_selected);
+
 static void scsi_sysfs_add_devices(struct Scsi_Host *shost)
 {
 	struct scsi_device *sdev;

drivers/scsi/scsi_transport_sas.c

@@ -40,8 +40,6 @@
 #include <scsi/scsi_transport_sas.h>
 
 #include "scsi_sas_internal.h"
-#include "scsi_priv.h"
-
 struct sas_host_attrs {
 	struct list_head rphy_list;
 	struct mutex lock;
@@ -1685,22 +1683,6 @@ int scsi_is_sas_rphy(const struct device *dev)
 }
 EXPORT_SYMBOL(scsi_is_sas_rphy);
 
-static void scan_channel_zero(struct Scsi_Host *shost, uint id, u64 lun)
-{
-	struct sas_host_attrs *sas_host = to_sas_host_attrs(shost);
-	struct sas_rphy *rphy;
-
-	list_for_each_entry(rphy, &sas_host->rphy_list, list) {
-		if (rphy->identify.device_type != SAS_END_DEVICE ||
-		    rphy->scsi_target_id == -1)
-			continue;
-
-		if (id == SCAN_WILD_CARD || id == rphy->scsi_target_id) {
-			scsi_scan_target(&rphy->dev, 0, rphy->scsi_target_id,
-					 lun, SCSI_SCAN_MANUAL);
-		}
-	}
-}
 
 /*
  * SCSI scan helper
@@ -1710,41 +1692,23 @@ static int sas_user_scan(struct Scsi_Host *shost, uint channel,
 		uint id, u64 lun)
 {
 	struct sas_host_attrs *sas_host = to_sas_host_attrs(shost);
-	int res = 0;
-	int i;
-
-	switch (channel) {
-	case 0:
-		mutex_lock(&sas_host->lock);
-		scan_channel_zero(shost, id, lun);
-		mutex_unlock(&sas_host->lock);
-		break;
-
-	case SCAN_WILD_CARD:
-		mutex_lock(&sas_host->lock);
-		scan_channel_zero(shost, id, lun);
-		mutex_unlock(&sas_host->lock);
+	struct sas_rphy *rphy;
 
-		for (i = 1; i <= shost->max_channel; i++) {
-			res = scsi_scan_host_selected(shost, i, id, lun,
-						      SCSI_SCAN_MANUAL);
-			if (res)
-				goto exit_scan;
-		}
-		break;
+	mutex_lock(&sas_host->lock);
+	list_for_each_entry(rphy, &sas_host->rphy_list, list) {
+		if (rphy->identify.device_type != SAS_END_DEVICE ||
+		    rphy->scsi_target_id == -1)
+			continue;
 
-	default:
-		if (channel <= shost->max_channel) {
-			res = scsi_scan_host_selected(shost, channel, id, lun,
-						      SCSI_SCAN_MANUAL);
-		} else {
-			res = -EINVAL;
+		if ((channel == SCAN_WILD_CARD || channel == 0) &&
+		    (id == SCAN_WILD_CARD || id == rphy->scsi_target_id)) {
+			scsi_scan_target(&rphy->dev, 0, rphy->scsi_target_id,
+					 lun, SCSI_SCAN_MANUAL);
 		}
-		break;
 	}
+	mutex_unlock(&sas_host->lock);
 
-exit_scan:
-	return res;
+	return 0;
 }