[RFC] [PATCH v2] MPC5121 TLB errata workaround

[David Jander]

Complete workaround for DTLB errata in MPC5121e processors of die M36P and 
older (all currently existing versions).

Due to the bug, the hardware-implemented LRU algorythm always goes to way 1 of 
the TLB. This fix implements the proposed software workaround in form of a LRW table for chosing the TLB-way.

Signed-off-by: David Jander <david at protonic.nl>

---
 arch/powerpc/kernel/head_32.S |   65 ++++++++++++++++++++++++++++++++++++++++
 1 files changed, 65 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index 0f4fac5..a88b3aa 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -540,6 +540,10 @@ DataLoadTLBMiss:
  * r2: ptr to linux-style pte
  * r3: scratch
  */
+#ifdef CONFIG_PPC_MPC512x
+       b      TlbWo    /* Code for TLB-errata workaround doesn't fit here */
+RFTlbWo:
+#endif
        mfctr   r0
        /* Get PTE (linux-style) and check access */
        mfspr   r3,SPRN_DMISS
@@ -612,6 +616,31 @@ DataStoreTLBMiss:
  * r2: ptr to linux-style pte
  * r3: scratch
  */
+#ifdef CONFIG_PPC_MPC512x
+/* MPC512x: workaround for errata in die M36P and earlier:
+ * Implement LRW for TLB way.
+ */
+       mfspr   r3,SPRN_DMISS
+       rlwinm  r3,r3,19,25,29 /* Get Address bits 19:15 */
+       lis     r2,lrw at ha       /* Search index in lrw[] */
+       addi    r2,r2,lrw at l
+       tophys(r2,r2)
+       lwzx    r1,r3,r2       /* Get item from lrw[] */
+       cmpwi   0,r1,0         /* Was it way 0 last time? */
+       beq-    0,113f         /* Then goto 113: */
+
+       mfspr   r1,SPRN_SRR1
+       rlwinm  r1,r1,0,15,13  /* Mask out SRR1[WAY] */
+       mtspr   SPRN_SRR1,r1
+
+       li      r0,0
+       stwx    r0,r3,r2       /* Make lrw[] entry 0 */
+       b       114f
+113:
+       li      r0,1
+       stwx    r0,r3,r2       /* Make lrw[] entry 1 */
+114:
+#endif
        mfctr   r0
        /* Get PTE (linux-style) and check access */
        mfspr   r3,SPRN_DMISS
@@ -688,6 +717,34 @@ DataStoreTLBMiss:
        .globl mol_trampoline
        .set mol_trampoline, i0x2f00

+#ifdef CONFIG_PPC_MPC512x
+TlbWo:
+/* MPC512x: workaround for errata in die M36P and earlier:
+ * Implement LRW for TLB way.
+ */
+       mfspr   r3,SPRN_DMISS
+       rlwinm  r3,r3,19,25,29 /* Get Address bits 19:15 */
+       lis     r2,lrw at ha       /* Search index in lrw[] */
+       addi    r2,r2,lrw at l
+       tophys(r2,r2)
+       lwzx    r1,r3,r2       /* Get item from lrw[] */
+       cmpwi   0,r1,0         /* Was it way 0 last time? */
+       beq-    0,113f         /* Then goto 113: */
+
+       mfspr   r1,SPRN_SRR1
+       rlwinm  r1,r1,0,15,13  /* Mask out SRR1[WAY] */
+       mtspr   SPRN_SRR1,r1
+
+       li      r0,0
+       stwx    r0,r3,r2       /* Make lrw[] entry 0 */
+       b       114f
+113:
+       li      r0,1
+       stwx    r0,r3,r2       /* Make lrw[] entry 1 */
+114:
+       b       RFTlbWo
+#endif
+
        . = 0x3000

 AltiVecUnavailable:
@@ -1321,6 +1378,14 @@ intercept_table:
        .long 0, 0, 0, 0, 0, 0, 0, 0
        .long 0, 0, 0, 0, 0, 0, 0, 0
        .long 0, 0, 0, 0, 0, 0, 0, 0
+
+#ifdef CONFIG_PPC_MPC512x
+lrw:
+       .long 0, 0, 0, 0, 0, 0, 0, 0
+       .long 0, 0, 0, 0, 0, 0, 0, 0
+       .long 0, 0, 0, 0, 0, 0, 0, 0
+       .long 0, 0, 0, 0, 0, 0, 0, 0
+#endif

 /* Room for two PTE pointers, usually the kernel and current user pointers
  * to their respective root page table.