powerpc: Disable /dev/port interface on systems without an ISA bridge

Some power systems do not have legacy ISA devices. So, /dev/port is not
a valid interface on these systems. User level tools such as kbdrate is
trying to access the device using this interface which is causing the
system crash.

This patch will fix this issue by not creating this interface on these
powerpc systems.
Signed-off-by: Haren Myneni <haren@us.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/io.h

@@ -20,6 +20,14 @@ extern int check_legacy_ioport(unsigned long base_port);
 #define _PNPWRP		0xa79
 #define PNPBIOS_BASE	0xf000
 
+#if defined(CONFIG_PPC64) && defined(CONFIG_PCI)
+extern struct pci_dev *isa_bridge_pcidev;
+/*
+ * has legacy ISA devices ?
+ */
+#define arch_has_dev_port()	(isa_bridge_pcidev != NULL)
+#endif
+
 #include <linux/device.h>
 #include <linux/io.h>
 

drivers/char/mem.c

@@ -27,14 +27,16 @@
 #include <linux/splice.h>
 #include <linux/pfn.h>
 #include <linux/export.h>
+#include <linux/io.h>
 
 #include <asm/uaccess.h>
-#include <asm/io.h>
 
 #ifdef CONFIG_IA64
 # include <linux/efi.h>
 #endif
 
+#define DEVPORT_MINOR	4
+
 static inline unsigned long size_inside_page(unsigned long start,
 					     unsigned long size)
 {
@@ -894,6 +896,13 @@ static int __init chr_dev_init(void)
 	for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
 		if (!devlist[minor].name)
 			continue;
+
+		/*
+		 * Create /dev/port? 
+		 */
+		if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
+			continue;
+
 		device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
 			      NULL, devlist[minor].name);
 	}

include/linux/io.h

@@ -67,4 +67,13 @@ int check_signature(const volatile void __iomem *io_addr,
 			const unsigned char *signature, int length);
 void devm_ioremap_release(struct device *dev, void *res);
 
+/*
+ * Some systems do not have legacy ISA devices.
+ * /dev/port is not a valid interface on these systems.
+ * So for those archs, <asm/io.h> should define the following symbol.
+ */
+#ifndef arch_has_dev_port
+#define arch_has_dev_port()     (1)
+#endif
+
 #endif /* _LINUX_IO_H */