powerpc/8xx: Update TLB asm so it behaves as linux mm expects.

Update the TLB asm to make proper use of _PAGE_DIRY and _PAGE_ACCESSED.
Get rid of _PAGE_HWWRITE too.
Pros:
 - I/D TLB Miss never needs to write to the linux pte.
 - _PAGE_ACCESSED is only set on TLB Error fixing accounting
 - _PAGE_DIRTY is mapped to 0x100, the changed bit, and is set directly
    when a page has been made dirty.
 - Proper RO/RW mapping of user space.
 - Free up 2 SW TLB bits in the linux pte(add back _PAGE_WRITETHRU ?)
 - kernel RO/user NA support.
Cons:
 - A few more instructions in the TLB Miss routines.

Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

2 files changed, 57 insertions, 55 deletions

diff --git a/arch/powerpc/include/asm/pte-8xx.h b/arch/powerpc/include/asm/pte-8xx.h
index dd5ea95fe61e..68ba861331ee 100644
--- a/arch/powerpc/include/asm/pte-8xx.h
+++ b/arch/powerpc/include/asm/pte-8xx.h
@@ -33,21 +33,20 @@
 #define _PAGE_NO_CACHE  0x0002  /* I: cache inhibit */
 #define _PAGE_SHARED    0x0004  /* No ASID (context) compare */
 #define _PAGE_SPECIAL   0x0008  /* SW entry, forced to 0 by the TLB miss */
+#define _PAGE_DIRTY     0x0100  /* C: page changed */
 
-/* These five software bits must be masked out when the entry is loaded
- * into the TLB.
+/* These 3 software bits must be masked out when the entry is loaded
+ * into the TLB, 2 SW bits left.
  */
 #define _PAGE_GUARDED   0x0010  /* software: guarded access */
-#define _PAGE_DIRTY     0x0020  /* software: page changed */
-#define _PAGE_RW        0x0040  /* software: user write access allowed */
-#define _PAGE_ACCESSED  0x0080  /* software: page referenced */
+#define _PAGE_ACCESSED  0x0020  /* software: page referenced */
 
 /* Setting any bits in the nibble with the follow two controls will
  * require a TLB exception handler change.  It is assumed unused bits
  * are always zero.
  */
-#define _PAGE_HWWRITE   0x0100  /* h/w write enable: never set in Linux PTE */
-#define _PAGE_USER      0x0800  /* One of the PP bits, the other is USER&~RW */
+#define _PAGE_RW        0x0400  /* lsb PP bits, inverted in HW */
+#define _PAGE_USER      0x0800  /* msb PP bits */
 
 #define _PMD_PRESENT    0x0001
 #define _PMD_BAD        0x0ff0
diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 6ded19d01891..97bd523a0278 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -333,26 +333,20 @@ 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
+        andi.   r11, r10, _PAGE_ACCESSED | _PAGE_PRESENT
+        cmpwi   cr0, r11, _PAGE_ACCESSED | _PAGE_PRESENT
+        bne-    cr0, 2f
+
+        /* Clear PP lsb, 0x400 */
+        rlwinm  r10, r10, 0, 22, 20
 
         /* The Linux PTE won't go exactly into the MMU TLB.
-         * Software indicator bits 21, 22 and 28 must be clear.
+         * Software indicator bits 22 and 28 must be clear.
          * Software indicator bits 24, 25, 26, and 27 must be
          * set.  All other Linux PTE bits control the behavior
          * of the MMU.
          */
-2:      li      r11, 0x00f0
+        li      r11, 0x00f0
         rlwimi  r10, r11, 0, 24, 28     /* Set 24-27, clear 28 */
         DO_8xx_CPU6(0x2d80, r3)
         mtspr   SPRN_MI_RPN, r10        /* Update TLB entry */
@@ -365,6 +359,22 @@ InstructionTLBMiss:
         lwz     r3, 8(r0)
 #endif
         rfi
+2:
+        mfspr   r11, SPRN_SRR1
+        /* clear all error bits as TLB Miss
+         * sets a few unconditionally
+        */
+        rlwinm  r11, r11, 0, 0xffff
+        mtspr   SPRN_SRR1, r11
+
+        mfspr   r10, SPRN_M_TW  /* Restore registers */
+        lwz     r11, 0(r0)
+        mtcr    r11
+        lwz     r11, 4(r0)
+#ifdef CONFIG_8xx_CPU6
+        lwz     r3, 8(r0)
+#endif
+        b       InstructionAccess
 
         . = 0x1200
 DataStoreTLBMiss:
@@ -409,21 +419,27 @@ DataStoreTLBMiss:
         DO_8xx_CPU6(0x3b80, r3)
         mtspr   SPRN_MD_TWC, r11
 
-#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)
+        /* Both _PAGE_ACCESSED and _PAGE_PRESENT has to be set.
+         * We also need to know if the insn is a load/store, so:
+         * Clear _PAGE_PRESENT and load that which will
+         * trap into DTLB Error with store bit set accordinly.
+         */
+        /* PRESENT=0x1, ACCESSED=0x20
+         * r11 = ((r10 & PRESENT) & ((r10 & ACCESSED) >> 5));
+         * r10 = (r10 & ~PRESENT) | r11;
+         */
+        rlwinm  r11, r10, 32-5, 31, 31
+        and     r11, r11, r10
+        rlwimi  r10, r11, 0, 31, 31
+
+        /* Honour kernel RO, User NA */
+        andi.   r11, r10, _PAGE_USER | _PAGE_RW
+        bne-    cr0, 5f
+        ori     r10,r10, 0x200 /* Extended encoding, bit 22 */
+5:      xori    r10, r10, _PAGE_RW  /* invert RW bit */
 
         /* The Linux PTE won't go exactly into the MMU TLB.
-         * Software indicator bits 21, 22 and 28 must be clear.
+         * Software indicator bits 22 and 28 must be clear.
          * Software indicator bits 24, 25, 26, and 27 must be
          * set.  All other Linux PTE bits control the behavior
          * of the MMU.
@@ -469,11 +485,12 @@ DataTLBError:
         stw     r10, 0(r0)
         stw     r11, 4(r0)
 
-        /* First, make sure this was a store operation.
+        mfspr   r11, SPRN_DSISR
+        andis.  r11, r11, 0x4800        /* !translation or protection */
+        bne     2f      /* branch if either is set */
+        /* Only Change bit left now, do it here as it is faster
+         * than trapping to the C fault handler.
         */
-        mfspr   r10, SPRN_DSISR
-        andis.  r11, r10, 0x0200        /* If set, indicates store op */
-        beq     2f
 
         /* The EA of a data TLB miss is automatically stored in the MD_EPN
          * register.  The EA of a data TLB error is automatically stored in
@@ -522,26 +539,12 @@ DataTLBError:
         mfspr   r11, SPRN_MD_TWC                /* ....and get the pte address */
         lwz     r10, 0(r11)             /* Get the pte */
 
-        andi.   r11, r10, _PAGE_RW      /* Is it writeable? */
-        beq     2f                      /* Bail out if not */
-
-        /* 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 */
+        ori     r10, r10, _PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_HWWRITE
         stw     r10, 0(r11)             /* and update pte in table */
+        xori    r10, r10, _PAGE_RW      /* RW bit is inverted */
 
         /* The Linux PTE won't go exactly into the MMU TLB.
-         * Software indicator bits 21, 22 and 28 must be clear.
+         * Software indicator bits 22 and 28 must be clear.
          * Software indicator bits 24, 25, 26, and 27 must be
          * set.  All other Linux PTE bits control the behavior
          * of the MMU.