[PATCH] ppc: L2 cache prefetch fixes on 745x

We run into problems if we blindly enable L2 prefetching without
checking that the L2 cache is actually enabled.  Additionaly, if we
disable the L2 cache we need to ensure that we disable L2 prefetching.

Signed-off-by: Kumar Gala <kumar.gala@freescale.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 34 insertions, 2 deletions

diff --git a/arch/ppc/kernel/cpu_setup_6xx.S b/arch/ppc/kernel/cpu_setup_6xx.S
index 468721d9ebd2..3fb1fb619d2c 100644
--- a/arch/ppc/kernel/cpu_setup_6xx.S
+++ b/arch/ppc/kernel/cpu_setup_6xx.S
@@ -249,8 +249,11 @@ END_FTR_SECTION_IFSET(CPU_FTR_NO_DPM)
         sync
         isync
 
-        /* Enable L2 HW prefetch
+        /* Enable L2 HW prefetch, if L2 is enabled
          */
+        mfspr   r3,SPRN_L2CR
+        andis.  r3,r3,L2CR_L2E@h
+        beqlr
         mfspr   r3,SPRN_MSSCR0
         ori     r3,r3,3
         sync
diff --git a/arch/ppc/kernel/l2cr.S b/arch/ppc/kernel/l2cr.S
index c39441048266..861115249b35 100644
--- a/arch/ppc/kernel/l2cr.S
+++ b/arch/ppc/kernel/l2cr.S
@@ -156,6 +156,26 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
                The bit moved on the 7450.....
           ****/
 
+BEGIN_FTR_SECTION
+        /* Disable L2 prefetch on some 745x and try to ensure
+         * L2 prefetch engines are idle. As explained by errata
+         * text, we can't be sure they are, we just hope very hard
+         * that well be enough (sic !). At least I noticed Apple
+         * doesn't even bother doing the dcbf's here...
+         */
+        mfspr   r4,SPRN_MSSCR0
+        rlwinm  r4,r4,0,0,29
+        sync
+        mtspr   SPRN_MSSCR0,r4
+        sync
+        isync
+        lis     r4,KERNELBASE@h
+        dcbf    0,r4
+        dcbf    0,r4
+        dcbf    0,r4
+        dcbf    0,r4
+END_FTR_SECTION_IFSET(CPU_FTR_SPEC7450)
+
         /* TODO: use HW flush assist when available */
 
         lis     r4,0x0002
@@ -230,7 +250,16 @@ END_FTR_SECTION_IFSET(CPU_FTR_SPEC7450)
         oris    r3,r3,0x8000
         mtspr   SPRN_L2CR,r3
         sync
-
+        
+        /* Enable L2 HW prefetch on 744x/745x */
+BEGIN_FTR_SECTION
+        mfspr   r3,SPRN_MSSCR0
+        ori     r3,r3,3
+        sync
+        mtspr   SPRN_MSSCR0,r3
+        sync
+        isync
+END_FTR_SECTION_IFSET(CPU_FTR_SPEC7450)
 4:
 
         /* Restore HID0[DPM] to whatever it was before */