From 091bc3a4049cb0cb28b8e3e71d8738387b91a007 Mon Sep 17 00:00:00 2001
From: Paul Burton <paul.burton@imgtec.com>
Date: Mon, 13 Jul 2015 17:12:44 +0100
Subject: [PATCH] MIPS: tlb-r4k: panic if the MMU doesn't support PAGE_SIZE
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After writing the appropriate mask to the cop0 PageMask register, read
the register back & check it matches what we want. If it doesn't then
the MMU does not support the page size the kernel is configured for and
we're better off bailing than continuing to do odd things with TLB
exceptions.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: Joshua Kinard <kumba@gentoo.org>
Cc: Rafał Miłecki <zajec5@gmail.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/10691/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
---
 arch/mips/mm/tlb-r4k.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/mips/mm/tlb-r4k.c b/arch/mips/mm/tlb-r4k.c
index 5037d5868cef..c17d7627f872 100644
--- a/arch/mips/mm/tlb-r4k.c
+++ b/arch/mips/mm/tlb-r4k.c
@@ -19,6 +19,7 @@
 #include <asm/cpu.h>
 #include <asm/cpu-type.h>
 #include <asm/bootinfo.h>
+#include <asm/hazards.h>
 #include <asm/mmu_context.h>
 #include <asm/pgtable.h>
 #include <asm/tlb.h>
@@ -486,6 +487,10 @@ static void r4k_tlb_configure(void)
 	 *     be set to fixed-size pages.
 	 */
 	write_c0_pagemask(PM_DEFAULT_MASK);
+	back_to_back_c0_hazard();
+	if (read_c0_pagemask() != PM_DEFAULT_MASK)
+		panic("MMU doesn't support PAGE_SIZE=0x%lx", PAGE_SIZE);
+
 	write_c0_wired(0);
 	if (current_cpu_type() == CPU_R10000 ||
 	    current_cpu_type() == CPU_R12000 ||
-- 
2.30.2