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Subject[PATCH 02/11] powerpc/8xx: remove tests on PGDIR entry validity
Date
Kernel MMU handling code handles validity of entries via _PMD_PRESENT which
corresponds to V bit in MD_TWC and MI_TWC. When the V bit is not set, MPC8xx
triggers TLBError exception. So we don't have to check that and branch ourself
to TLBError. We can set TLB entries with non present entries, remove all those
tests and let the 8xx handle it. This reduce the number of cycle when the
entries are valid which is the case most of the time, and doesn't significantly
increase the time for handling invalid entries.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

---
arch/powerpc/kernel/head_8xx.S | 41 ++++++++---------------------------------
1 file changed, 8 insertions(+), 33 deletions(-)

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 79b8a23..2c329f1 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -329,12 +329,9 @@ InstructionTLBMiss:
/* Extract level 1 index */
rlwinm r10, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
lwzx r11, r10, r11 /* Get the level 1 entry */
- rlwinm. r10, r11,0,0,19 /* Extract page descriptor page address */
- beq 2f /* If zero, don't try to find a pte */
+ rlwinm r10, r11,0,0,19 /* Extract page descriptor page address */

- /* We have a pte table, so load the MI_TWC with the attributes
- * for this "segment."
- */
+ /* Load the MI_TWC with the attributes for this "segment." */
MTSPR_CPU6(SPRN_MI_TWC, r11, r3) /* Set segment attributes */
mfspr r11, SPRN_SRR0 /* Get effective address of fault */
/* Extract level 2 index */
@@ -342,13 +339,11 @@ InstructionTLBMiss:
lwzx r10, r10, r11 /* Get the pte */

#ifdef CONFIG_SWAP
- andi. r11, r10, _PAGE_ACCESSED | _PAGE_PRESENT
- cmpwi cr0, r11, _PAGE_ACCESSED | _PAGE_PRESENT
- li r11, RPN_PATTERN
- bne- cr0, 2f
-#else
- li r11, RPN_PATTERN
+ rlwinm r11, r10, 32-5, _PAGE_PRESENT
+ and r11, r11, r10
+ rlwimi r10, r11, 0, _PAGE_PRESENT
#endif
+ li r11, RPN_PATTERN
/* The Linux PTE won't go exactly into the MMU TLB.
* Software indicator bits 21 and 28 must be clear.
* Software indicator bits 24, 25, 26, and 27 must be
@@ -366,21 +361,6 @@ InstructionTLBMiss:
mfspr r10, SPRN_SPRG_SCRATCH2
EXCEPTION_EPILOG_0
rfi
-2:
- mfspr r10, SPRN_SRR1
- /* clear all error bits as TLB Miss
- * sets a few unconditionally
- */
- rlwinm r10, r10, 0, 0xffff
- mtspr SPRN_SRR1, r10
-
- /* Restore registers */
-#ifdef CONFIG_8xx_CPU6
- mfspr r3, SPRN_DAR
- mtspr SPRN_DAR, r11 /* Tag DAR */
-#endif
- mfspr r10, SPRN_SPRG_SCRATCH2
- b InstructionTLBError1

. = 0x1200
DataStoreTLBMiss:
@@ -403,8 +383,6 @@ DataStoreTLBMiss:
/* Extract level 1 index */
rlwinm r10, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
lwzx r11, r10, r11 /* Get the level 1 entry */
- rlwinm. r10, r11,0,0,19 /* Extract page descriptor page address */
- beq 2f /* If zero, don't try to find a pte */

/* We have a pte table, so load fetch the pte from the table.
*/
@@ -450,7 +428,7 @@ DataStoreTLBMiss:
* set. All other Linux PTE bits control the behavior
* of the MMU.
*/
-2: li r11, RPN_PATTERN
+ li r11, RPN_PATTERN
rlwimi r10, r11, 0, 24, 28 /* Set 24-27, clear 28 */
MTSPR_CPU6(SPRN_MD_RPN, r10, r3) /* Update TLB entry */

@@ -469,10 +447,7 @@ DataStoreTLBMiss:
*/
. = 0x1300
InstructionTLBError:
- EXCEPTION_PROLOG_0
-InstructionTLBError1:
- EXCEPTION_PROLOG_1
- EXCEPTION_PROLOG_2
+ EXCEPTION_PROLOG
mr r4,r12
mr r5,r9
andis. r10,r5,0x4000
--
2.1.0


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