MIPS: Implement __read_mostly

Just do what everyone else is doing by placing __read_mostly things in
the .data.read_mostly section.

mips_io_port_base can not be read-only (const) and writable
(__read_mostly) at the same time. One of them has to go, so I chose
to eliminate the __read_mostly. It will still get stuck in a portion
of memory that is not adjacent to things that are written, and thus
not be on a dirty cache line, for whatever that is worth.

Signed-off-by: David Daney <[e-mail]>
To: [e-mail]
Patchwork: http://patchwork.linux-mips.org/patch/1702/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/include/asm/cache.h

···
 #define SMP_CACHE_SHIFT		L1_CACHE_SHIFT
 #define SMP_CACHE_BYTES		L1_CACHE_BYTES
 
+#define __read_mostly __attribute__((__section__(".data.read_mostly")))
+
 #endif /* _ASM_CACHE_H */

arch/mips/kernel/setup.c

···
  * mips_io_port_base is the begin of the address space to which x86 style
  * I/O ports are mapped.
  */
-const unsigned long mips_io_port_base __read_mostly = -1;
+const unsigned long mips_io_port_base = -1;
 EXPORT_SYMBOL(mips_io_port_base);
 
 static struct resource code_resource = { .name = "Kernel code", };