MIPS: Take in account load hazards for HI/LO restoring

MIPS CPUs usually have 1 to 4 cycles load hazards, thus doing load
and right after move to HI/LO will usually stall the pipeline for
significant amount of time. Let's take it into account and separate
loads and mthi/lo in instruction sequence.

The patch uses t6 and t7 registers as temporaries in addition to t8.

The patch tries to deal with SmartMIPS, but I know little about and
haven't tested it.

Changes in v2:
- clear separation of actions for SmartMIPS and pre-MIPSR6.

Signed-off-by: Siarhei Volkau <lis8215@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

diff --git a/arch/mips/include/asm/stackframe.h b/arch/mips/include/asm/stackframe.h
index a8705aef47e12d7af5a43c04ada66e07ec886dff..a13431379073f29ae327935386b7590b61594335 100644 (file)
--- a/arch/mips/include/asm/stackframe.h
+++ b/arch/mips/include/asm/stackframe.h
@@ -308,17 +308,12 @@
                jal     octeon_mult_restore
 #endif
 #ifdef CONFIG_CPU_HAS_SMARTMIPS
-               LONG_L  $24, PT_ACX(sp)
-               mtlhx   $24
-               LONG_L  $24, PT_HI(sp)
-               mtlhx   $24
+               LONG_L  $14, PT_ACX(sp)
                LONG_L  $24, PT_LO(sp)
-               mtlhx   $24
+               LONG_L  $15, PT_HI(sp)
 #elif !defined(CONFIG_CPU_MIPSR6)
                LONG_L  $24, PT_LO(sp)
-               mtlo    $24
-               LONG_L  $24, PT_HI(sp)
-               mthi    $24
+               LONG_L  $15, PT_HI(sp)
 #endif
 #ifdef CONFIG_32BIT
                cfi_ld  $8, PT_R8, \docfi
@@ -327,6 +322,14 @@
                cfi_ld  $10, PT_R10, \docfi
                cfi_ld  $11, PT_R11, \docfi
                cfi_ld  $12, PT_R12, \docfi
+#ifdef CONFIG_CPU_HAS_SMARTMIPS
+               mtlhx   $14
+               mtlhx   $15
+               mtlhx   $24
+#elif !defined(CONFIG_CPU_MIPSR6)
+               mtlo    $24
+               mthi    $15
+#endif
                cfi_ld  $13, PT_R13, \docfi
                cfi_ld  $14, PT_R14, \docfi
                cfi_ld  $15, PT_R15, \docfi