1 files changed, 33 insertions, 24 deletions

diff --git a/arch/arc/mm/tlb.c b/arch/arc/mm/tlb.c
index 8ceefbf72fb0..4097764fea23 100644
--- a/arch/arc/mm/tlb.c
+++ b/arch/arc/mm/tlb.c
@@ -762,21 +762,23 @@ void read_decode_mmu_bcr(void)
         tmp = read_aux_reg(ARC_REG_MMU_BCR);
         mmu->ver = (tmp >> 24);
 
-        if (mmu->ver <= 2) {
-                mmu2 = (struct bcr_mmu_1_2 *)&tmp;
-                mmu->pg_sz_k = TO_KB(0x2000);
-                mmu->sets = 1 << mmu2->sets;
-                mmu->ways = 1 << mmu2->ways;
-                mmu->u_dtlb = mmu2->u_dtlb;
-                mmu->u_itlb = mmu2->u_itlb;
-        } else if (mmu->ver == 3) {
-                mmu3 = (struct bcr_mmu_3 *)&tmp;
-                mmu->pg_sz_k = 1 << (mmu3->pg_sz - 1);
-                mmu->sets = 1 << mmu3->sets;
-                mmu->ways = 1 << mmu3->ways;
-                mmu->u_dtlb = mmu3->u_dtlb;
-                mmu->u_itlb = mmu3->u_itlb;
-                mmu->sasid = mmu3->sasid;
+        if (is_isa_arcompact()) {
+                if (mmu->ver <= 2) {
+                        mmu2 = (struct bcr_mmu_1_2 *)&tmp;
+                        mmu->pg_sz_k = TO_KB(0x2000);
+                        mmu->sets = 1 << mmu2->sets;
+                        mmu->ways = 1 << mmu2->ways;
+                        mmu->u_dtlb = mmu2->u_dtlb;
+                        mmu->u_itlb = mmu2->u_itlb;
+                } else {
+                        mmu3 = (struct bcr_mmu_3 *)&tmp;
+                        mmu->pg_sz_k = 1 << (mmu3->pg_sz - 1);
+                        mmu->sets = 1 << mmu3->sets;
+                        mmu->ways = 1 << mmu3->ways;
+                        mmu->u_dtlb = mmu3->u_dtlb;
+                        mmu->u_itlb = mmu3->u_itlb;
+                        mmu->sasid = mmu3->sasid;
+                }
         } else {
                 mmu4 = (struct bcr_mmu_4 *)&tmp;
                 mmu->pg_sz_k = 1 << (mmu4->sz0 - 1);
@@ -818,8 +820,9 @@ int pae40_exist_but_not_enab(void)
 
 void arc_mmu_init(void)
 {
-        char str[256];
         struct cpuinfo_arc_mmu *mmu = &cpuinfo_arc700[smp_processor_id()].mmu;
+        char str[256];
+        int compat = 0;
 
         pr_info("%s", arc_mmu_mumbojumbo(0, str, sizeof(str)));
 
@@ -834,15 +837,21 @@ void arc_mmu_init(void)
          */
         BUILD_BUG_ON(!IS_ALIGNED(STACK_TOP, PMD_SIZE));
 
-        /* For efficiency sake, kernel is compile time built for a MMU ver
-         * This must match the hardware it is running on.
-         * Linux built for MMU V2, if run on MMU V1 will break down because V1
-         *  hardware doesn't understand cmds such as WriteNI, or IVUTLB
-         * On the other hand, Linux built for V1 if run on MMU V2 will do
-         *   un-needed workarounds to prevent memcpy thrashing.
-         * Similarly MMU V3 has new features which won't work on older MMU
+        /*
+         * Ensure that MMU features assumed by kernel exist in hardware.
+         * For older ARC700 cpus, it has to be exact match, since the MMU
+         * revisions were not backwards compatible (MMUv3 TLB layout changed
+         * so even if kernel for v2 didn't use any new cmds of v3, it would
+         * still not work.
+         * For HS cpus, MMUv4 was baseline and v5 is backwards compatible
+         * (will run older software).
          */
-        if (mmu->ver != CONFIG_ARC_MMU_VER) {
+        if (is_isa_arcompact() && mmu->ver == CONFIG_ARC_MMU_VER)
+                compat = 1;
+        else if (is_isa_arcv2() && mmu->ver >= CONFIG_ARC_MMU_VER)
+                compat = 1;
+
+        if (!compat) {
                 panic("MMU ver %d doesn't match kernel built for %d...\n",
                       mmu->ver, CONFIG_ARC_MMU_VER);
         }