s390/pci: add parameter to disable usage of MIO instructions

Allow users to disable usage of MIO instructions by specifying pci=nomio
at the kernel command line.

Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -3395,6 +3395,7 @@
 				this removes isolation between devices and
 				may put more devices in an IOMMU group.
 		force_floating	[S390] Force usage of floating interrupts.
+		nomio		[S390] Do not use MIO instructions.
 
 	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power
 			Management.

arch/s390/pci/pci.c

@@ -850,6 +850,7 @@ static void zpci_mem_exit(void)
 }
 
 static unsigned int s390_pci_probe __initdata = 1;
+static unsigned int s390_pci_no_mio __initdata;
 unsigned int s390_pci_force_floating __initdata;
 static unsigned int s390_pci_initialized;
 
@@ -859,6 +860,10 @@ char * __init pcibios_setup(char *str)
 		s390_pci_probe = 0;
 		return NULL;
 	}
+	if (!strcmp(str, "nomio")) {
+		s390_pci_no_mio = 1;
+		return NULL;
+	}
 	if (!strcmp(str, "force_floating")) {
 		s390_pci_force_floating = 1;
 		return NULL;
@@ -881,7 +886,7 @@ static int __init pci_base_init(void)
 	if (!test_facility(69) || !test_facility(71))
 		return 0;
 
-	if (test_facility(153))
+	if (test_facility(153) && !s390_pci_no_mio)
 		static_branch_enable(&have_mio);
 
 	rc = zpci_debug_init();