[POWERPC] 8xx: fix swap

This makes swap routines operate correctly on the ppc_8xx based machines.
Code has been revalidated on mpc885ads (8M sdram) with recent kernel. Based
on patch from Yuri Tikhonov <yur@emcraft.com> to do the same on arch/ppc
instance.

Recent kernel's size makes swap feature very important on low-memory platforms,
those are actually non-operable without it.
Signed-off-by: Yuri Tikhonov <yur@emcraft.com>
Signed-off-by: Vitaly Bordug <vitb@kernel.crashing.org>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/kernel/head_8xx.S

@@ -332,8 +332,18 @@ InstructionTLBMiss:
 	mfspr	r11, SPRN_MD_TWC	/* ....and get the pte address */
 	lwz	r10, 0(r11)	/* Get the pte */
 
+#ifdef CONFIG_SWAP
+	/* do not set the _PAGE_ACCESSED bit of a non-present page */
+	andi.	r11, r10, _PAGE_PRESENT
+	beq	4f
+	ori	r10, r10, _PAGE_ACCESSED
+	mfspr	r11, SPRN_MD_TWC	/* get the pte address again */
+	stw	r10, 0(r11)
+4:
+#else
 	ori	r10, r10, _PAGE_ACCESSED
 	stw	r10, 0(r11)
+#endif
 
 	/* The Linux PTE won't go exactly into the MMU TLB.
 	 * Software indicator bits 21, 22 and 28 must be clear.
@@ -398,8 +408,17 @@ DataStoreTLBMiss:
 	DO_8xx_CPU6(0x3b80, r3)
 	mtspr	SPRN_MD_TWC, r11
 
-	mfspr	r11, SPRN_MD_TWC	/* get the pte address again */
+#ifdef CONFIG_SWAP
+	/* do not set the _PAGE_ACCESSED bit of a non-present page */
+	andi.	r11, r10, _PAGE_PRESENT
+	beq	4f
 	ori	r10, r10, _PAGE_ACCESSED
+4:
+	/* and update pte in table */
+#else
+	ori	r10, r10, _PAGE_ACCESSED
+#endif
+	mfspr	r11, SPRN_MD_TWC	/* get the pte address again */
 	stw	r10, 0(r11)
 
 	/* The Linux PTE won't go exactly into the MMU TLB.
@@ -507,7 +526,16 @@ DataTLBError:
 
 	/* Update 'changed', among others.
 	*/
+#ifdef CONFIG_SWAP
+	ori	r10, r10, _PAGE_DIRTY|_PAGE_HWWRITE
+	/* do not set the _PAGE_ACCESSED bit of a non-present page */
+	andi.	r11, r10, _PAGE_PRESENT
+	beq	4f
+	ori	r10, r10, _PAGE_ACCESSED
+4:
+#else
 	ori	r10, r10, _PAGE_DIRTY|_PAGE_ACCESSED|_PAGE_HWWRITE
+#endif
 	mfspr	r11, SPRN_MD_TWC		/* Get pte address again */
 	stw	r10, 0(r11)		/* and update pte in table */
 

include/asm-powerpc/pgtable-ppc32.h

@@ -339,14 +339,6 @@ extern int icache_44x_need_flush;
 #define _PMD_PAGE_MASK	0x000c
 #define _PMD_PAGE_8M	0x000c
 
-/*
- * The 8xx TLB miss handler allegedly sets _PAGE_ACCESSED in the PTE
- * for an address even if _PAGE_PRESENT is not set, as a performance
- * optimization.  This is a bug if you ever want to use swap unless
- * _PAGE_ACCESSED is 2, which it isn't, or unless you have 8xx-specific
- * definitions for __swp_entry etc. below, which would be gross.
- *  -- paulus
- */
 #define _PTE_NONE_MASK _PAGE_ACCESSED
 
 #else /* CONFIG_6xx */