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>

1 files changed, 8 insertions, 0 deletions

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 */