[PATCH v2 05/11] powerpc/8xx: Optimise access to swapper_pg_dir

From: Christophe Leroy
Date: Tue Jan 20 2015 - 05:09:07 EST


All accessed to PGD entries are done via 0(r11).
By using lower part of swapper_pg_dir as load index to r11, we can remove the
ori instruction.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>

---
v2: fixed/added comments to explain what is the real content of M_TW

arch/powerpc/kernel/head_8xx.S | 35 +++++++++++++++++++----------------
1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index ae05f28..a485ad7 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -319,16 +319,15 @@ InstructionTLBMiss:
* pin the first 8MB of kernel memory */
andis. r11, r10, 0x8000 /* Address >= 0x80000000 */
#endif
- mfspr r11, SPRN_M_TW /* Get level 1 table base address */
+ mfspr r11, SPRN_M_TW /* Get level 1 table */
#ifdef CONFIG_MODULES
beq 3f
- lis r11, (swapper_pg_dir-PAGE_OFFSET)@h
- ori r11, r11, (swapper_pg_dir-PAGE_OFFSET)@l
+ lis r11, (swapper_pg_dir-PAGE_OFFSET)@ha
3:
#endif
/* Insert level 1 index */
rlwimi r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
- lwz r11, 0(r11) /* Get the level 1 entry */
+ lwz r11, (swapper_pg_dir-PAGE_OFFSET)@l(r11) /* Get the level 1 entry */

/* Load the MI_TWC with the attributes for this "segment." */
MTSPR_CPU6(SPRN_MI_TWC, r11, r3) /* Set segment attributes */
@@ -374,14 +373,13 @@ DataStoreTLBMiss:
* kernel page tables.
*/
andis. r11, r10, 0x8000
- mfspr r11, SPRN_M_TW /* Get level 1 table base address */
+ mfspr r11, SPRN_M_TW /* Get level 1 table */
beq 3f
- lis r11, (swapper_pg_dir-PAGE_OFFSET)@h
- ori r11, r11, (swapper_pg_dir-PAGE_OFFSET)@l
+ lis r11, (swapper_pg_dir-PAGE_OFFSET)@ha
3:
/* Insert level 1 index */
rlwimi r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
- lwz r11, 0(r11) /* Get the level 1 entry */
+ lwz r11, (swapper_pg_dir-PAGE_OFFSET)@l(r11) /* Get the level 1 entry */

/* We have a pte table, so load fetch the pte from the table.
*/
@@ -509,13 +507,12 @@ FixupDAR:/* Entry point for dcbx workaround. */
/* fetch instruction from memory. */
mfspr r10, SPRN_SRR0
andis. r11, r10, 0x8000 /* Address >= 0x80000000 */
- mfspr r11, SPRN_M_TW /* Get level 1 table base address */
- beq- 3f /* Branch if user space */
- lis r11, (swapper_pg_dir-PAGE_OFFSET)@h
- ori r11, r11, (swapper_pg_dir-PAGE_OFFSET)@l
+ mfspr r11, SPRN_M_TW /* Get level 1 table */
+ beq 3f
+ lis r11, (swapper_pg_dir-PAGE_OFFSET)@ha
/* Insert level 1 index */
3: rlwimi r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
- lwz r11, 0(r11) /* Get the level 1 entry */
+ lwz r11, (swapper_pg_dir-PAGE_OFFSET)@l(r11) /* Get the level 1 entry */
rlwinm r11, r11,0,0,19 /* Extract page descriptor page address */
/* Insert level 2 index */
rlwimi r11, r10, 32 - (PAGE_SHIFT - 2), 32 - PAGE_SHIFT, 29
@@ -670,8 +667,7 @@ start_here:
* init's THREAD like the context switch code does, but this is
* easier......until someone changes init's static structures.
*/
- lis r6, swapper_pg_dir@h
- ori r6, r6, swapper_pg_dir@l
+ lis r6, swapper_pg_dir@ha
tophys(r6,r6)
#ifdef CONFIG_8xx_CPU6
lis r4, cpu6_errata_word@h
@@ -850,6 +846,13 @@ _GLOBAL(set_context)
stw r4, 0x4(r5)
#endif

+ /* Register M_TW will contain base address of level 1 table minus the
+ * lower part of the kernel PGDIR base address, so that all accesses to
+ * level 1 table are done relative to lower part of kernel PGDIR base
+ * address.
+ */
+ li r5, (swapper_pg_dir-PAGE_OFFSET)@l
+ sub r4, r4, r5
#ifdef CONFIG_8xx_CPU6
lis r6, cpu6_errata_word@h
ori r6, r6, cpu6_errata_word@l
@@ -857,7 +860,7 @@ _GLOBAL(set_context)
li r7, 0x3f80
stw r7, 12(r6)
lwz r7, 12(r6)
- mtspr SPRN_M_TW, r4 /* Update MMU base address */
+ mtspr SPRN_M_TW, r4 /* Update pointeur to level 1 table */
li r7, 0x3380
stw r7, 12(r6)
lwz r7, 12(r6)
--
2.1.0

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