MIPS: mm: Fix broken microMIPS kernel regression.

Commit f4ae17aa0f2122b52f642985b46210a1f2eceb0a [MIPS: mm: Use scratch for
PGD when !CONFIG_MIPS_PGD_C0_CONTEXT] broke microMIPS kernel builds. This
patch refactors that code similar to what was done for the 'clear_page'
and 'copy_page' functions.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6744/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/tlb-funcs.S

@@ -16,8 +16,10 @@
 
 #define FASTPATH_SIZE	128
 
+EXPORT(tlbmiss_handler_setup_pgd_start)
 LEAF(tlbmiss_handler_setup_pgd)
-	.space		16 * 4
+1:	j	1b		/* Dummy, will be replaced. */
+	.space	64
 END(tlbmiss_handler_setup_pgd)
 EXPORT(tlbmiss_handler_setup_pgd_end)
 

arch/mips/mm/tlbex.c

@@ -1422,16 +1422,17 @@ static void build_r4000_tlb_refill_handler(void)
 extern u32 handle_tlbl[], handle_tlbl_end[];
 extern u32 handle_tlbs[], handle_tlbs_end[];
 extern u32 handle_tlbm[], handle_tlbm_end[];
-extern u32 tlbmiss_handler_setup_pgd[], tlbmiss_handler_setup_pgd_end[];
+extern u32 tlbmiss_handler_setup_pgd_start[], tlbmiss_handler_setup_pgd[];
+extern u32 tlbmiss_handler_setup_pgd_end[];
 
 static void build_setup_pgd(void)
 {
 	const int a0 = 4;
 	const int __maybe_unused a1 = 5;
 	const int __maybe_unused a2 = 6;
-	u32 *p = tlbmiss_handler_setup_pgd;
+	u32 *p = tlbmiss_handler_setup_pgd_start;
 	const int tlbmiss_handler_setup_pgd_size =
-		tlbmiss_handler_setup_pgd_end - tlbmiss_handler_setup_pgd;
+		tlbmiss_handler_setup_pgd_end - tlbmiss_handler_setup_pgd_start;
 #ifndef CONFIG_MIPS_PGD_C0_CONTEXT
 	long pgdc = (long)pgd_current;
 #endif