From: Jesper Nilsson <jesper.nilsson@axis.com>
Date: Fri, 25 Jan 2008 17:05:12 +0000 (+0100)
Subject: CRIS v32: Add workaround for MMU hardware bug for ETRAX FS in mm/mmu.S
X-Git-Tag: v2.6.25-rc1~40^2~45
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3d44305abe1fe75793a4b42de51d8a0be9bedc3f;p=linux-2.6

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

diff --git a/arch/cris/arch-v32/mm/mmu.S b/arch/cris/arch-v32/mm/mmu.S
index 27b70e5006..2238d154bd 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