powerpc/8xx: Restore _PAGE_WRITETHRU

8xx has not had WRITETHRU due to lack of bits in the pte.
After the recent rewrite of the 8xx TLB code, there are
two bits left. Use one of them to WRITETHRU.

Perhaps use the last SW bit to PAGE_SPECIAL or PAGE_FILE?

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

2 files changed, 11 insertions, 2 deletions

diff --git a/arch/powerpc/include/asm/pte-8xx.h b/arch/powerpc/include/asm/pte-8xx.h
index 68ba861331ee..d44826e4ff97 100644
--- a/arch/powerpc/include/asm/pte-8xx.h
+++ b/arch/powerpc/include/asm/pte-8xx.h
@@ -35,11 +35,12 @@
 #define _PAGE_SPECIAL   0x0008  /* SW entry, forced to 0 by the TLB miss */
 #define _PAGE_DIRTY     0x0100  /* C: page changed */
 
-/* These 3 software bits must be masked out when the entry is loaded
- * into the TLB, 2 SW bits left.
+/* These 4 software bits must be masked out when the entry is loaded
+ * into the TLB, 1 SW bit left(0x0080).
  */
 #define _PAGE_GUARDED   0x0010  /* software: guarded access */
 #define _PAGE_ACCESSED  0x0020  /* software: page referenced */
+#define _PAGE_WRITETHRU 0x0040  /* software: caching is write through */
 
 /* Setting any bits in the nibble with the follow two controls will
  * require a TLB exception handler change.  It is assumed unused bits
diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 1a28ee8ca318..c4ae85b8f8c0 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -422,6 +422,10 @@ DataStoreTLBMiss:
          * above.
          */
         rlwimi  r11, r10, 0, 27, 27
+        /* Insert the WriteThru flag into the TWC from the Linux PTE.
+         * It is bit 25 in the Linux PTE and bit 30 in the TWC
+         */
+        rlwimi  r11, r10, 32-5, 30, 30
         DO_8xx_CPU6(0x3b80, r3)
         mtspr   SPRN_MD_TWC, r11
 
@@ -559,6 +563,10 @@ DARFixed:/* Return from dcbx instruction bug workaround, r10 holds value of DAR
          * It is bit 27 of both the Linux PTE and the TWC
          */
         rlwimi  r11, r10, 0, 27, 27
+        /* Insert the WriteThru flag into the TWC from the Linux PTE.
+         * It is bit 25 in the Linux PTE and bit 30 in the TWC
+         */
+        rlwimi  r11, r10, 32-5, 30, 30
         DO_8xx_CPU6(0x3b80, r3)
         mtspr   SPRN_MD_TWC, r11
         mfspr   r11, SPRN_MD_TWC        /* get the pte address again */