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>

1 files changed, 6 insertions, 7 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