diff --git a/hw/esp.c b/hw/esp.c
index 8e17005..0ebc181 100644
--- a/hw/esp.c
+++ b/hw/esp.c
@@ -723,7 +723,8 @@ void esp_init(target_phys_addr_t espaddr, int it_shift,
 
 static const struct SCSIBusInfo esp_scsi_info = {
     .tcq = false,
-    .ndev = ESP_MAX_DEVS,
+    .max_target = ESP_MAX_DEVS,
+    .max_lun = 7,
 
     .transfer_data = esp_transfer_data,
     .complete = esp_command_complete,
diff --git a/hw/lsi53c895a.c b/hw/lsi53c895a.c
index c15f167..d26e442 100644
--- a/hw/lsi53c895a.c
+++ b/hw/lsi53c895a.c
@@ -2085,7 +2085,8 @@ static int lsi_scsi_uninit(PCIDevice *d)
 
 static const struct SCSIBusInfo lsi_scsi_info = {
     .tcq = true,
-    .ndev = LSI_MAX_DEVS,
+    .max_target = LSI_MAX_DEVS,
+    .max_lun = 0,  /* LUN support is buggy */
 
     .transfer_data = lsi_transfer_data,
     .complete = lsi_command_complete,
diff --git a/hw/scsi-bus.c b/hw/scsi-bus.c
index a2d57a7..cec06db 100644
--- a/hw/scsi-bus.c
+++ b/hw/scsi-bus.c
@@ -17,7 +17,7 @@ static struct BusInfo scsi_bus_info = {
     .get_fw_dev_path = scsibus_get_fw_dev_path,
     .props = (Property[]) {
         DEFINE_PROP_UINT32("scsi-id", SCSIDevice, id, -1),
-        DEFINE_PROP_UINT32("lun", SCSIDevice, lun, 0),
+        DEFINE_PROP_UINT32("lun", SCSIDevice, lun, -1),
         DEFINE_PROP_END_OF_LIST(),
     },
 };
@@ -37,26 +37,42 @@ static int scsi_qdev_init(DeviceState *qdev, DeviceInfo *base)
     SCSIDevice *dev = DO_UPCAST(SCSIDevice, qdev, qdev);
     SCSIDeviceInfo *info = DO_UPCAST(SCSIDeviceInfo, qdev, base);
     SCSIBus *bus = DO_UPCAST(SCSIBus, qbus, dev->qdev.parent_bus);
-    SCSIDevice *olddev;
+    SCSIDevice *d;
     int rc = -1;
 
-    if (dev->id == -1) {
-        int id;
-        for (id = 0; id < bus->info->ndev; id++) {
-            if (!scsi_device_find(bus, id, 0)) {
-                dev->id = id;
-                break;
-            }
-        }
-    }
-    if (dev->id >= bus->info->ndev) {
+    if (dev->id != -1 && dev->id > bus->info->max_target) {
         error_report("bad scsi device id: %d", dev->id);
         goto err;
     }
 
-    olddev = scsi_device_find(bus, dev->id, dev->lun);
-    if (olddev && dev->lun == olddev->lun) {
-        qdev_free(&olddev->qdev);
+    if (dev->id == -1) {
+        int id = -1;
+        if (dev->lun == -1) {
+            dev->lun = 0;
+        }
+        do {
+            d = scsi_device_find(bus, ++id, dev->lun);
+        } while (d && d->lun == dev->lun && id <= bus->info->max_target);
+        if (id > bus->info->max_target) {
+            error_report("no free target");
+            goto err;
+        }
+        dev->id = id;
+    } else if (dev->lun == -1) {
+        int lun = -1;
+        do {
+            d = scsi_device_find(bus, dev->id, ++lun);
+        } while (d && d->lun == lun && lun < bus->info->max_lun);
+        if (lun > bus->info->max_lun) {
+            error_report("no free lun");
+            goto err;
+        }
+        dev->lun = lun;
+    } else {
+        d = scsi_device_find(bus, dev->id, dev->lun);
+        if (dev->lun == d->lun && dev != d) {
+            qdev_free(&d->qdev);
+        }
     }
 
     dev->info = info;
@@ -115,7 +131,7 @@ int scsi_bus_legacy_handle_cmdline(SCSIBus *bus)
     int res = 0, unit;
 
     loc_push_none(&loc);
-    for (unit = 0; unit < bus->info->ndev; unit++) {
+    for (unit = 0; unit < bus->info->max_target; unit++) {
         dinfo = drive_get(IF_SCSI, bus->busnr, unit);
         if (dinfo == NULL) {
             continue;
diff --git a/hw/scsi.h b/hw/scsi.h
index add3d2d..401d8d3 100644
--- a/hw/scsi.h
+++ b/hw/scsi.h
@@ -98,7 +98,8 @@ struct SCSIDeviceInfo {
 };
 
 struct SCSIBusInfo {
-    int tcq, ndev;
+    int tcq;
+    int max_target, max_lun;
     void (*transfer_data)(SCSIRequest *req, uint32_t arg);
     void (*complete)(SCSIRequest *req, uint32_t arg);
     void (*cancel)(SCSIRequest *req);
diff --git a/hw/spapr_vscsi.c b/hw/spapr_vscsi.c
index aae845a..334b2e6 100644
--- a/hw/spapr_vscsi.c
+++ b/hw/spapr_vscsi.c
@@ -131,9 +131,39 @@ static void vscsi_put_req(vscsi_req *req)
 
 static SCSIDevice *vscsi_device_find(SCSIBus *bus, uint64_t srp_lun, int *lun)
 {
-    /* XXX Figure that one out properly ! This is crackpot */
-    int id = (srp_lun >> 56) & 0x7f;
-    *lun = (srp_lun >> 48) & 0xff;
+    int channel = 0, id = 0;
+
+retry:
+    switch (srp_lun >> 62) {
+    case 0:
+        if ((srp_lun >> 56) != 0) {
+            channel = (srp_lun >> 56) & 0x3f;
+            id = (srp_lun >> 48) & 0xff;
+            srp_lun <<= 16;
+            goto retry;
+        }
+        *lun = (srp_lun >> 48) & 0xff;
+        break;
+
+    case 1:
+        *lun = (srp_lun >> 48) & 0x3fff;
+        break;
+    case 2:
+        channel = (srp_lun >> 53) & 0x7;
+        id = (srp_lun >> 56) & 0x3f;
+        *lun = (srp_lun >> 48) & 0x1f;
+        break;
+    case 3:
+        *lun = -1;
+        return NULL;
+    default:
+        abort();
+    }
+
+    if (channel) {
+        *lun = -1;
+        return NULL;
+    }
     return scsi_device_find (bus, id, *lun);
 }
 
@@ -862,7 +892,8 @@ static int vscsi_do_crq(struct VIOsPAPRDevice *dev, uint8_t *crq_data)
 
 static const struct SCSIBusInfo vscsi_scsi_info = {
     .tcq = true,
-    .ndev = 63, /* logical unit addressing format */
+    .max_target = 63, /* logical unit addressing format */
+    .max_lun = 31,
 
     .transfer_data = vscsi_transfer_data,
     .complete = vscsi_command_complete,
diff --git a/hw/usb-msd.c b/hw/usb-msd.c
index d0e0cd3..2d88596 100644
--- a/hw/usb-msd.c
+++ b/hw/usb-msd.c
@@ -494,7 +494,8 @@ static void usb_msd_password_cb(void *opaque, int err)
 
 static const struct SCSIBusInfo usb_msd_scsi_info = {
     .tcq = false,
-    .ndev = 1,
+    .max_target = 0,
+    .max_lun = 0,
 
     .transfer_data = usb_msd_transfer_data,
     .complete = usb_msd_command_complete,
