s390: make PCI mio support a machine flag

[ Upstream commit 3322ba0 ]

Kernel support for the newer PCI mio instructions can be toggled off
with the pci=nomio command line option which needs to integrate with
common code PCI option parsing. However this option then toggles static
branches which can't be toggled yet in an early_param() call.

Thus commit 9964f39 ("s390: fix setting of mio addressing control")
moved toggling the static branches to the PCI init routine.

With this setup however we can't check for mio support outside the PCI
code during early boot, i.e. before switching the static branches, which
we need to be able to export this as an ELF HWCAP.

Improve on this by turning mio availability into a machine flag that
gets initially set based on CONFIG_PCI and the facility bit and gets
toggled off if pci=nomio is found during PCI option parsing allowing
simple access to this machine flag after early init.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/s390/include/asm/setup.h

@@ -36,6 +36,7 @@
 #define MACHINE_FLAG_NX		BIT(15)
 #define MACHINE_FLAG_GS		BIT(16)
 #define MACHINE_FLAG_SCC	BIT(17)
+#define MACHINE_FLAG_PCI_MIO	BIT(18)
 
 #define LPP_MAGIC		BIT(31)
 #define LPP_PID_MASK		_AC(0xffffffff, UL)
@@ -110,6 +111,7 @@ extern unsigned long mio_wb_bit_mask;
 #define MACHINE_HAS_NX		(S390_lowcore.machine_flags & MACHINE_FLAG_NX)
 #define MACHINE_HAS_GS		(S390_lowcore.machine_flags & MACHINE_FLAG_GS)
 #define MACHINE_HAS_SCC		(S390_lowcore.machine_flags & MACHINE_FLAG_SCC)
+#define MACHINE_HAS_PCI_MIO	(S390_lowcore.machine_flags & MACHINE_FLAG_PCI_MIO)
 
 /*
  * Console mode. Override with conmode=

arch/s390/kernel/early.c

@@ -236,6 +236,10 @@ static __init void detect_machine_facilities(void)
 		clock_comparator_max = -1ULL >> 1;
 		__ctl_set_bit(0, 53);
 	}
+	if (IS_ENABLED(CONFIG_PCI) && test_facility(153)) {
+		S390_lowcore.machine_flags |= MACHINE_FLAG_PCI_MIO;
+		/* the control bit is set during PCI initialization */
+	}
 }
 
 static inline void save_vector_registers(void)

arch/s390/pci/pci.c

@@ -893,7 +893,6 @@ 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;
 
@@ -904,7 +903,7 @@ char * __init pcibios_setup(char *str)
 		return NULL;
 	}
 	if (!strcmp(str, "nomio")) {
-		s390_pci_no_mio = 1;
+		S390_lowcore.machine_flags &= ~MACHINE_FLAG_PCI_MIO;
 		return NULL;
 	}
 	if (!strcmp(str, "force_floating")) {
@@ -935,7 +934,7 @@ static int __init pci_base_init(void)
 		return 0;
 	}
 
-	if (test_facility(153) && !s390_pci_no_mio) {
+	if (MACHINE_HAS_PCI_MIO) {
 		static_branch_enable(&have_mio);
 		ctl_set_bit(2, 5);
 	}