Re: [PATCH 00/13] powerpc: Backport 8xx TLB to 2.4

Scott Wood [off-list ref] wrote on 2011/01/13 21:44:00:

quoted

BTW, it occurred to me that the following 8xx quirk is best
done in 8xx code:

From c1985a3b8b16d96ddce5ef90d5a15e70fb8a2aec Mon Sep 17 00:00:00 2001
From: Joakim Tjernlund <redacted>
Date: Tue, 11 Jan 2011 11:24:22 +0100
Subject: [PATCH] 8xx: Move invalidation of non present TLBs

8xx does not invalidate ~PRESENT TLBs, move the workaround
in mm/fault.c here to keep 8xx quirks localized.

Signed-off-by: Joakim Tjernlund <redacted>
---
 arch/ppc/kernel/head_8xx.S |   12 ++++++++++--
 arch/ppc/mm/fault.c        |    7 -------
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/ppc/kernel/head_8xx.S b/arch/ppc/kernel/head_8xx.S
index 75acaa0..24b206c 100644
--- a/arch/ppc/kernel/head_8xx.S
+++ b/arch/ppc/kernel/head_8xx.S

@@ -221,7 +221,11 @@ DataAccess:
    mr   r5,r20
    mfspr   r4,DAR
    stw   r4,_DAR(r21)
-   li   r20,0x00f0
+   /* invalidate ~PRESENT TLBs, 8xx MMU don't do this */
+   andis.   r20,r5,0x4000
+   beq+   1f
+   tlbie   r4
+1:   li   r20,0x00f
    mtspr   DAR,r20   /* Tag DAR */
    addi   r3,r1,STACK_FRAME_OVERHEAD
    li   r20,MSR_KERNEL

@@ -238,7 +242,11 @@ InstructionAccess:
    addi   r3,r1,STACK_FRAME_OVERHEAD
    mr   r4,r22
    mr   r5,r23
-   li   r20,MSR_KERNEL
+   /* invalidate ~PRESENT TLBs, 8xx MMU don't do this */
+   andis.   r20,r5,0x4000
+   beq+   1f
+   tlbie   r4
+1:   li   r20,MSR_KERNEL
    rlwimi   r20,r23,0,16,16      /* copy EE bit from saved MSR */
    FINISH_EXCEPTION(do_page_fault)

diff --git a/arch/ppc/mm/fault.c b/arch/ppc/mm/fault.c
index 874005a..8819fb1 100644
--- a/arch/ppc/mm/fault.c
+++ b/arch/ppc/mm/fault.c

@@ -116,13 +116,6 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
    else
       is_write = error_code & 0x02000000;
 #endif /* CONFIG_4xx || CONFIG_BOOKE */
-#if defined(CONFIG_8xx)
-   /* 8xx does no invalidate TLBs that are ~PRESENT,
-    * do it here.
-    */
-   if (error_code & 0x40000000)
-      _tlbie(address);
-#endif
 #if defined(CONFIG_XMON) || defined(CONFIG_KGDB)
    if (debugger_fault_handler && regs->trap == 0x300) {
       debugger_fault_handler(regs);
--

1.7.3.4

Scott, what do you think of this? Is it safe to call tlbie in this context?

I'd guess so (I assume the concern is MMU translation being off?), but I
don't have any particular knowledge about this.  I'd be checking the
same manual that you have. :-)

I noticed 2.6 uses tlbie in CPU15 errata workaround so it is fine
and it is better to invalidate as soon as possible to free up a TLB slot.
Runs on my old 2.4 too.

 Jocke