[SCSI] ibmvscsi: Make max_requests module parameter more accurate

In a previous patch to fix an issue with error recovery,
the behavior of the max_requests module paramater was also
changed. If, for some reason, max_requests is set to one by
the user, we will end up with a negative number for can_queue.
Fix this by making max_requests not include the two event structs
needed to do error recovery.
Signed-off-by: NBrian King <brking@linux.vnet.ibm.com>
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/ibmvscsi/ibmvscsi.c

@@ -89,6 +89,7 @@ static int max_id = 64;
 static int max_channel = 3;
 static int init_timeout = 5;
 static int max_requests = IBMVSCSI_MAX_REQUESTS_DEFAULT;
+static int max_events = IBMVSCSI_MAX_REQUESTS_DEFAULT + 2;
 
 static struct scsi_transport_template *ibmvscsi_transport_template;
 
@@ -1633,7 +1634,7 @@ static struct scsi_host_template driver_template = {
 static unsigned long ibmvscsi_get_desired_dma(struct vio_dev *vdev)
 {
 	/* iu_storage data allocated in initialize_event_pool */
-	unsigned long desired_io = max_requests * sizeof(union viosrp_iu);
+	unsigned long desired_io = max_events * sizeof(union viosrp_iu);
 
 	/* add io space for sg data */
 	desired_io += (IBMVSCSI_MAX_SECTORS_DEFAULT * 512 *
@@ -1657,7 +1658,6 @@ static int ibmvscsi_probe(struct vio_dev *vdev, const struct vio_device_id *id)
 
 	vdev->dev.driver_data = NULL;
 
-	driver_template.can_queue = max_requests - 2;
 	host = scsi_host_alloc(&driver_template, sizeof(*hostdata));
 	if (!host) {
 		dev_err(&vdev->dev, "couldn't allocate host data\n");
@@ -1673,12 +1673,12 @@ static int ibmvscsi_probe(struct vio_dev *vdev, const struct vio_device_id *id)
 	atomic_set(&hostdata->request_limit, -1);
 	hostdata->host->max_sectors = IBMVSCSI_MAX_SECTORS_DEFAULT;
 
-	rc = ibmvscsi_ops->init_crq_queue(&hostdata->queue, hostdata, max_requests);
+	rc = ibmvscsi_ops->init_crq_queue(&hostdata->queue, hostdata, max_events);
 	if (rc != 0 && rc != H_RESOURCE) {
 		dev_err(&vdev->dev, "couldn't initialize crq. rc=%d\n", rc);
 		goto init_crq_failed;
 	}
-	if (initialize_event_pool(&hostdata->pool, max_requests, hostdata) != 0) {
+	if (initialize_event_pool(&hostdata->pool, max_events, hostdata) != 0) {
 		dev_err(&vdev->dev, "couldn't initialize event pool\n");
 		goto init_pool_failed;
 	}
@@ -1730,7 +1730,7 @@ static int ibmvscsi_probe(struct vio_dev *vdev, const struct vio_device_id *id)
       add_host_failed:
 	release_event_pool(&hostdata->pool, hostdata);
       init_pool_failed:
-	ibmvscsi_ops->release_crq_queue(&hostdata->queue, hostdata, max_requests);
+	ibmvscsi_ops->release_crq_queue(&hostdata->queue, hostdata, max_events);
       init_crq_failed:
 	scsi_host_put(host);
       scsi_host_alloc_failed:
@@ -1742,7 +1742,7 @@ static int ibmvscsi_remove(struct vio_dev *vdev)
 	struct ibmvscsi_host_data *hostdata = vdev->dev.driver_data;
 	release_event_pool(&hostdata->pool, hostdata);
 	ibmvscsi_ops->release_crq_queue(&hostdata->queue, hostdata,
-					max_requests);
+					max_events);
 
 	srp_remove_host(hostdata->host);
 	scsi_remove_host(hostdata->host);
@@ -1779,6 +1779,10 @@ int __init ibmvscsi_module_init(void)
 {
 	int ret;
 
+	/* Ensure we have two requests to do error recovery */
+	driver_template.can_queue = max_requests;
+	max_events = max_requests + 2;
+
 	if (firmware_has_feature(FW_FEATURE_ISERIES))
 		ibmvscsi_ops = &iseriesvscsi_ops;
 	else if (firmware_has_feature(FW_FEATURE_VIO))