scsi: zfcp: make DIX experimental, disabled, and independent of DIF

Introduce separate zfcp module parameters to individually select support
for: DIF which should work (zfcp.dif, which used to be DIF+DIX, disabled)
or DIX+DIF which can cause trouble (zfcp.dix, new, disabled).

If DIX is enabled, we warn on zfcp driver initialization.  As before, this
also reduces the maximum I/O request size to half, to support the worst
case of merged single sector requests with one protection data scatter
gather element per sector. This can impact the maximum throughput.

In DIF-only mode (zfcp.dif=1 zfcp.dix=0), we can use the full maximum I/O
request size as there is no protection data for zfcp.
Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Fedor Loshakov <loshakov@linux.ibm.com>
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/s390/scsi/zfcp_aux.c

@@ -124,6 +124,9 @@ static int __init zfcp_module_init(void)
 {
 	int retval = -ENOMEM;
 
+	if (zfcp_experimental_dix)
+		pr_warn("DIX is enabled. It is experimental and might cause problems\n");
+
 	zfcp_fsf_qtcb_cache = zfcp_cache_hw_align("zfcp_fsf_qtcb",
 						  sizeof(struct fsf_qtcb));
 	if (!zfcp_fsf_qtcb_cache)

drivers/s390/scsi/zfcp_ext.h

@@ -146,6 +146,7 @@ extern void zfcp_qdio_close(struct zfcp_qdio *);
 extern void zfcp_qdio_siosl(struct zfcp_adapter *);
 
 /* zfcp_scsi.c */
+extern bool zfcp_experimental_dix;
 extern struct scsi_transport_template *zfcp_scsi_transport_template;
 extern int zfcp_scsi_adapter_register(struct zfcp_adapter *);
 extern void zfcp_scsi_adapter_unregister(struct zfcp_adapter *);

drivers/s390/scsi/zfcp_scsi.c

@@ -27,7 +27,11 @@ MODULE_PARM_DESC(queue_depth, "Default queue depth for new SCSI devices");
 
 static bool enable_dif;
 module_param_named(dif, enable_dif, bool, 0400);
-MODULE_PARM_DESC(dif, "Enable DIF/DIX data integrity support");
+MODULE_PARM_DESC(dif, "Enable DIF data integrity support (default off)");
+
+bool zfcp_experimental_dix;
+module_param_named(dix, zfcp_experimental_dix, bool, 0400);
+MODULE_PARM_DESC(dix, "Enable experimental DIX (data integrity extension) support which implies DIF support (default off)");
 
 static bool allow_lun_scan = true;
 module_param(allow_lun_scan, bool, 0600);
@@ -790,11 +794,11 @@ void zfcp_scsi_set_prot(struct zfcp_adapter *adapter)
 	data_div = atomic_read(&adapter->status) &
 		   ZFCP_STATUS_ADAPTER_DATA_DIV_ENABLED;
 
-	if (enable_dif &&
+	if ((enable_dif || zfcp_experimental_dix) &&
 	    adapter->adapter_features & FSF_FEATURE_DIF_PROT_TYPE1)
 		mask |= SHOST_DIF_TYPE1_PROTECTION;
 
-	if (enable_dif && data_div &&
+	if (zfcp_experimental_dix && data_div &&
 	    adapter->adapter_features & FSF_FEATURE_DIX_PROT_TCPIP) {
 		mask |= SHOST_DIX_TYPE1_PROTECTION;
 		scsi_host_set_guard(shost, SHOST_DIX_GUARD_IP);