CRIS v32: Add workaround for MMU hardware bug for ETRAX FS in mm/mmu.S

1 files changed, 81 insertions, 12 deletions

diff --git a/arch/cris/arch-v32/mm/mmu.S b/arch/cris/arch-v32/mm/mmu.S
index 27b70e5006af..2238d154bde3 100644
--- a/arch/cris/arch-v32/mm/mmu.S
+++ b/arch/cris/arch-v32/mm/mmu.S
@@ -1,3 +1,5 @@
+; WARNING : The refill handler has been modified, see below !!!
+
 /*
  *  Copyright (C) 2003 Axis Communications AB
  *
@@ -61,6 +63,14 @@
 ; Note that the code is optimized to minimize stalls (makes the code harder
 ; to read).
 ;
+; WARNING !!!
+; Modified by Mikael Asker 060725: added a workaround for strange TLB
+; behavior. If the same PTE is present in more than one set, the TLB
+; doesn't recognize it and we get stuck in a loop of refill exceptions.
+; The workaround detects such loops and exits them by flushing
+; the TLB contents. The problem and workaround were verified
+; in VCS by Mikael Starvik.
+;
 ; Each page is 8 KB. Each PMD holds 8192/4 PTEs (each PTE is 4 bytes) so each
 ; PMD holds 16 MB of virtual memory.
 ;   Bits  0-12 : Offset within a page
@@ -68,6 +78,11 @@
 ;   Bits 24-31 : PMD offset within the PGD
 
 .macro MMU_REFILL_HANDLER handler, mmu
+        .data
+1:      .dword  0               ; refill_count
+                                ;   == 0 <=> last_refill_cause is invalid
+2:      .dword  0               ; last_refill_cause
+        .text
         .globl \handler
 \handler:
         subq    4, $sp
@@ -76,42 +91,96 @@
         subq    4, $sp
         move    \mmu, $srs      ; Select MMU support register bank
         move.d  $acr, [$sp]
-        subq    4, $sp
-        move.d  $r0, [$sp]
+        subq    12, $sp
+        move.d  1b, $acr        ; Point to refill_count
+        movem   $r2, [$sp]
+
+        test.d  [$acr]          ; refill_count == 0 ?
+        beq     5f              ;   yes, last_refill_cause is invalid
+        move.d  $acr, $r1
+
+        ; last_refill_cause is valid, investigate cause
+        addq    4, $r1          ; Point to last_refill_cause
+        move    $s3, $r0        ; Get rw_mm_cause
+        move.d  [$r1], $r2      ; Get last_refill_cause
+        cmp.d   $r0, $r2        ; rw_mm_cause == last_refill_cause ?
+        beq     6f              ;   yes, increment count
+        moveq   1, $r2
+
+        ; rw_mm_cause != last_refill_cause
+        move.d  $r2, [$acr]     ; refill_count = 1
+        move.d  $r0, [$r1]      ; last_refill_cause = rw_mm_cause
+
+3:      ; Probably not in a loop, continue normal processing
 #ifdef CONFIG_SMP
         move    $s7, $acr       ; PGD
 #else
         move.d  per_cpu__current_pgd, $acr ; PGD
 #endif
         ; Look up PMD in PGD
-        move    $s3, $r0        ; rw_mm_cause
         lsrq    24, $r0 ; Get PMD index into PGD (bit 24-31)
         move.d  [$acr], $acr    ; PGD for the current process
         addi    $r0.d, $acr, $acr
         move    $s3, $r0        ; rw_mm_cause
         move.d  [$acr], $acr    ; Get PMD
-        beq     1f
+        beq     8f
         ; Look up PTE in PMD
         lsrq    PAGE_SHIFT, $r0
         and.w   PAGE_MASK, $acr ; Remove PMD flags
         and.d   0x7ff, $r0      ; Get PTE index into PMD (bit 13-23)
         addi    $r0.d, $acr, $acr
         move.d  [$acr], $acr    ; Get PTE
-        beq     2f
-        move.d  [$sp+], $r0     ; Pop r0 in delayslot
+        beq     9f
+        movem   [$sp], $r2      ; Restore r0-r2 in delay slot
+        addq    12, $sp
         ; Store in TLB
         move    $acr, $s5
-        ; Return
+4:      ; Return
         move.d  [$sp+], $acr
-        move    [$sp], $srs
+        move    [$sp], $srs
         addq    4, $sp
         rete
         rfe
-1:      ; PMD missing, let the mm subsystem fix it up.
-        move.d  [$sp+], $r0     ; Pop r0
-2:      ; PTE missing, let the mm subsystem fix it up.
+
+5:      ; last_refill_cause is invalid
+        moveq   1, $r2
+        addq    4, $r1          ; Point to last_refill_cause
+        move.d  $r2, [$acr]     ; refill_count = 1
+        move    $s3, $r0        ; Get rw_mm_cause
+        ba      3b              ; Continue normal processing
+        move.d  $r0,[$r1]       ; last_refill_cause = rw_mm_cause
+
+6:      ; rw_mm_cause == last_refill_cause
+        move.d  [$acr], $r2     ; Get refill_count
+        cmpq    4, $r2          ; refill_count > 4 ?
+        bhi     7f              ;   yes
+        addq    1, $r2          ; refill_count++
+        ba      3b              ; Continue normal processing
+        move.d  $r2, [$acr]
+
+7:      ; refill_count > 4, error
+        move.d  $acr, $r0       ; Save pointer to refill_count
+        clear.d [$r0]           ; refill_count = 0
+
+        ;; rewind the short stack
+        movem   [$sp], $r2      ; Restore r0-r2
+        addq    12, $sp
+        move.d  [$sp+], $acr
+        move    [$sp], $srs
+        addq    4, $sp
+        ;; Keep it simple (slow), save all the regs.
+        SAVE_ALL
+        jsr     __flush_tlb_all
+        nop
+        ba      ret_from_intr   ; Return
+        nop
+
+8:      ; PMD missing, let the mm subsystem fix it up.
+        movem   [$sp], $r2      ; Restore r0-r2
+9:      ; PTE missing, let the mm subsystem fix it up.
+        addq    12, $sp
         move.d  [$sp+], $acr
-        move    [$sp], $srs
+        move    [$sp], $srs
         addq    4, $sp
         SAVE_ALL
         move    \mmu, $srs