x86: Add two helper macros for fixed address mapping

Sometimes fixmap will be used to map an physical address which
is not PAGE align, so to use it we need first map it and then
add the address offset to the mapped fixed address. These 2 new
helpers are suggested by Ingo Molnar to make the process
simpler.

For a physicall address like "phys", a directly usable virtual
address can be get by
	virt = (void *)set_fixmap_offset(fixed_idx, phys);
or
	virt = (void *)set_fixmap_offset_nocache(fixed_idx, phys);
(depends on whether the physical address is cachable or not).
Signed-off-by: NFeng Tang <feng.tang@intel.com>
Cc: alan@linux.intel.com
Cc: greg@kroah.com
Cc: x86@kernel.org
LKML-Reference: <1284361736-23011-3-git-send-email-feng.tang@intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/include/asm/fixmap.h

@@ -214,5 +214,20 @@ static inline unsigned long virt_to_fix(const unsigned long vaddr)
 	BUG_ON(vaddr >= FIXADDR_TOP || vaddr < FIXADDR_START);
 	return __virt_to_fix(vaddr);
 }
+
+/* Return an pointer with offset calculated */
+static inline unsigned long __set_fixmap_offset(enum fixed_addresses idx,
+				phys_addr_t phys, pgprot_t flags)
+{
+	__set_fixmap(idx, phys, flags);
+	return fix_to_virt(idx) + (phys & (PAGE_SIZE - 1));
+}
+
+#define set_fixmap_offset(idx, phys)			\
+	__set_fixmap_offset(idx, phys, PAGE_KERNEL)
+
+#define set_fixmap_offset_nocache(idx, phys)			\
+	__set_fixmap_offset(idx, phys, PAGE_KERNEL_NOCACHE)
+
 #endif /* !__ASSEMBLY__ */
 #endif /* _ASM_X86_FIXMAP_H */