MIPS: Enable IOREMAP_PROT config option for MIPS cpus

Allows the users of ptrace to access memory mapped by the ptraced process
using the same cache coherency attributes as the original process.
For example while using gdb with ioremap_prot() incorporated, both gdb and
the process being traced will have same cache coherency attributes.

Signed-off-by: Hassan Naveed <[e-mail]>
Signed-off-by: Paul Burton <[e-mail]>
Patchwork: https://patchwork.linux-mips.org/patch/20955/
Cc: <[e-mail]>

Documentation/features/vm/ioremap_prot/arch-support.txt

···
     |        ia64: | TODO |
     |        m68k: | TODO |
     |  microblaze: | TODO |
-    |        mips: | TODO |
+    |        mips: |  ok  |
     |       nds32: | TODO |
     |       nios2: | TODO |
     |    openrisc: | TODO |

arch/mips/Kconfig

···
 	select HAVE_FUNCTION_TRACER
 	select HAVE_GENERIC_DMA_COHERENT
 	select HAVE_IDE
+	select HAVE_IOREMAP_PROT
 	select HAVE_IRQ_EXIT_ON_IRQ_STACK
 	select HAVE_IRQ_TIME_ACCOUNTING
 	select HAVE_KPROBES

arch/mips/include/asm/io.h

···
 }
 
 /*
+ * ioremap_prot     -   map bus memory into CPU space
+ * @offset:    bus address of the memory
+ * @size:      size of the resource to map
+
+ * ioremap_prot gives the caller control over cache coherency attributes (CCA)
+ */
+static inline void __iomem *ioremap_prot(phys_addr_t offset,
+		unsigned long size, unsigned long prot_val) {
+	return __ioremap_mode(offset, size, prot_val & _CACHE_MASK);
+}
+
+/*
  * ioremap     -   map bus memory into CPU space
  * @offset:    bus address of the memory
  * @size:      size of the resource to map

arch/mips/include/asm/page.h

···
 typedef struct { unsigned long pgprot; } pgprot_t;
 #define pgprot_val(x)	((x).pgprot)
 #define __pgprot(x)	((pgprot_t) { (x) } )
+#define pte_pgprot(x)	__pgprot(pte_val(x) & ~_PFN_MASK)
 
 /*
  * On R4000-style MMUs where a TLB entry is mapping a adjacent even / odd