ARM: io: add a default IO_SPACE_LIMIT definition

Add a default IO_SPACE_LIMIT definition.  Explain the chosen value and
suggest why platforms would want to make it larger.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/io.h

@@ -109,6 +109,27 @@ static inline void __iomem *__typesafe_io(unsigned long addr)
  */
 #include <mach/io.h>
 
+/*
+ * This is the limit of PC card/PCI/ISA IO space, which is by default
+ * 64K if we have PC card, PCI or ISA support.  Otherwise, default to
+ * zero to prevent ISA/PCI drivers claiming IO space (and potentially
+ * oopsing.)
+ *
+ * Only set this larger if you really need inb() et.al. to operate over
+ * a larger address space.  Note that SOC_COMMON ioremaps each sockets
+ * IO space area, and so inb() et.al. must be defined to operate as per
+ * readb() et.al. on such platforms.
+ */
+#ifndef IO_SPACE_LIMIT
+#if defined(CONFIG_PCMCIA_SOC_COMMON) || defined(CONFIG_PCMCIA_SOC_COMMON_MODULE)
+#define IO_SPACE_LIMIT ((resource_size_t)0xffffffff)
+#elif defined(CONFIG_PCI) || defined(CONFIG_ISA) || defined(CONFIG_PCCARD)
+#define IO_SPACE_LIMIT ((resource_size_t)0xffff)
+#else
+#define IO_SPACE_LIMIT ((resource_size_t)0)
+#endif
+#endif
+
 /*
  *  IO port access primitives
  *  -------------------------