powerpc/8xx: make user addr DTLB miss the short path

User space DTLB miss represent approximatly 90% of TLB misses
so make it the shortest path.

Also remove an unneccessary double jump in FixupDAR

Before this patch, we spend 3.3 TB ticks in the handler for each
user address miss and 3.4 TB ticks for each kernel address miss
After this patch, we send 3.0 TB ticks in the handler for each
user address miss and 3.9 TB ticks for each kernel address miss
Taking into account that user misses represent 90% of the total,
this patch provides an improvement of approx. 9%

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <oss@buserror.net>

1 files changed, 23 insertions, 30 deletions

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index f674dfae1e95..033a6b735487 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -382,30 +382,31 @@ InstructionTLBMiss:
 
         . = 0x1200
 DataStoreTLBMiss:
+        mtspr   SPRN_SPRG_SCRATCH2, r3
         EXCEPTION_PROLOG_0
-        mfcr    r10
+        mfcr    r3
 
         /* If we are faulting a kernel address, we have to use the
          * kernel page tables.
          */
-        mfspr   r11, SPRN_MD_EPN
-        rlwinm  r11, r11, 16, 0xfff8
+        mfspr   r10, SPRN_MD_EPN
+        rlwinm  r10, r10, 16, 0xfff8
+        cmpli   cr0, r10, PAGE_OFFSET@h
+        mfspr   r11, SPRN_M_TW  /* Get level 1 table */
+        blt+    3f
 #ifndef CONFIG_PIN_TLB_IMMR
-        cmpli   cr0, r11, VIRT_IMMR_BASE@h
+        cmpli   cr0, r10, VIRT_IMMR_BASE@h
 #endif
-        cmpli   cr7, r11, PAGE_OFFSET@h
+_ENTRY(DTLBMiss_cmp)
+        cmpli   cr7, r10, (PAGE_OFFSET + 0x1800000)@h
+        lis     r11, (swapper_pg_dir-PAGE_OFFSET)@ha
 #ifndef CONFIG_PIN_TLB_IMMR
 _ENTRY(DTLBMiss_jmp)
         beq-    DTLBMissIMMR
 #endif
-        bge-    cr7, DTLBMissLinear
-
-        mfspr   r11, SPRN_M_TW  /* Get level 1 table */
+        blt     cr7, DTLBMissLinear
 3:
-        mtcr    r10
-#ifdef CONFIG_8xx_CPU6
-        mtspr   SPRN_SPRG_SCRATCH2, r3
-#endif
+        mtcr    r3
         mfspr   r10, SPRN_MD_EPN
 
         /* Insert level 1 index */
@@ -458,9 +459,7 @@ _ENTRY(DTLBMiss_jmp)
         MTSPR_CPU6(SPRN_MD_RPN, r10, r3)        /* Update TLB entry */
 
         /* Restore registers */
-#ifdef CONFIG_8xx_CPU6
         mfspr   r3, SPRN_SPRG_SCRATCH2
-#endif
         mtspr   SPRN_DAR, r11   /* Tag DAR */
         EXCEPTION_EPILOG_0
         rfi
@@ -531,7 +530,7 @@ DARFixed:/* Return from dcbx instruction bug workaround */
  * not enough space in the DataStoreTLBMiss area.
  */
 DTLBMissIMMR:
-        mtcr    r10
+        mtcr    r3
         /* Set 512k byte guarded page and mark it valid */
         li      r10, MD_PS512K | MD_GUARDED | MD_SVALID
         MTSPR_CPU6(SPRN_MD_TWC, r10, r11)
@@ -543,27 +542,23 @@ DTLBMissIMMR:
 
         li      r11, RPN_PATTERN
         mtspr   SPRN_DAR, r11   /* Tag DAR */
+        mfspr   r3, SPRN_SPRG_SCRATCH2
         EXCEPTION_EPILOG_0
         rfi
 
 DTLBMissLinear:
-_ENTRY(DTLBMiss_cmp)
-        cmpli   cr0, r11, (PAGE_OFFSET + 0x1800000)@h
-        lis     r11, (swapper_pg_dir-PAGE_OFFSET)@ha
-        bge-    3b
-
-        mtcr    r10
+        mtcr    r3
         /* Set 8M byte page and mark it valid */
-        li      r10, MD_PS8MEG | MD_SVALID
-        MTSPR_CPU6(SPRN_MD_TWC, r10, r11)
-        mfspr   r10, SPRN_MD_EPN
-        rlwinm  r10, r10, 0, 0x0f800000         /* 8xx supports max 256Mb RAM */
+        li      r11, MD_PS8MEG | MD_SVALID
+        MTSPR_CPU6(SPRN_MD_TWC, r11, r3)
+        rlwinm  r10, r10, 16, 0x0f800000        /* 8xx supports max 256Mb RAM */
         ori     r10, r10, 0xf0 | MD_SPS16K | _PAGE_SHARED | _PAGE_DIRTY | \
                           _PAGE_PRESENT
         MTSPR_CPU6(SPRN_MD_RPN, r10, r11)       /* Update TLB entry */
 
         li      r11, RPN_PATTERN
         mtspr   SPRN_DAR, r11   /* Tag DAR */
+        mfspr   r3, SPRN_SPRG_SCRATCH2
         EXCEPTION_EPILOG_0
         rfi
 
@@ -583,7 +578,9 @@ FixupDAR:/* Entry point for dcbx workaround. */
         rlwinm  r11, r10, 16, 0xfff8
 _ENTRY(FixupDAR_cmp)
         cmpli   cr7, r11, (PAGE_OFFSET + 0x1800000)@h
-        blt-    cr7, 200f
+        /* create physical page address from effective address */
+        tophys(r11, r10)
+        blt-    cr7, 201f
         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
@@ -613,10 +610,6 @@ _ENTRY(FixupDAR_cmp)
 141:    mfspr   r10,SPRN_SPRG_SCRATCH2
         b       DARFixed        /* Nope, go back to normal TLB processing */
 
-        /* create physical page address from effective address */
-200:    tophys(r11, r10)
-        b       201b
-
 144:    mfspr   r10, SPRN_DSISR
         rlwinm  r10, r10,0,7,5  /* Clear store bit for buggy dcbst insn */
         mtspr   SPRN_DSISR, r10