ARM: convert all "mov.* pc, reg" to "bx reg" for ARMv6+

ARMv6 and greater introduced a new instruction ("bx") which can be used
to return from function calls.  Recent CPUs perform better when the
"bx lr" instruction is used rather than the "mov pc, lr" instruction,
and this sequence is strongly recommended to be used by the ARM
architecture manual (section A.4.1.1).

We provide a new macro "ret" with all its variants for the condition
code which will resolve to the appropriate instruction.

Rather than doing this piecemeal, and miss some instances, change all
the "mov pc" instances to use the new macro, with the exception of
the "movs" instruction and the kprobes code.  This allows us to detect
the "mov pc, lr" case and fix it up - and also gives us the possibility
of deploying this for other registers depending on the CPU selection.

Reported-by: Will Deacon <will.deacon@arm.com>
Tested-by: Stephen Warren <swarren@nvidia.com> # Tegra Jetson TK1
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr> # mioa701_bootresume.S
Tested-by: Andrew Lunn <andrew@lunn.ch> # Kirkwood
Tested-by: Shawn Guo <shawn.guo@freescale.com>
Tested-by: Tony Lindgren <tony@atomide.com> # OMAPs
Tested-by: Gregory CLEMENT <gregory.clement@free-electrons.com> # Armada XP, 375, 385
Acked-by: Sekhar Nori <nsekhar@ti.com> # DaVinci
Acked-by: Christoffer Dall <christoffer.dall@linaro.org> # kvm/hyp
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com> # PXA3xx
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> # Xen
Tested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> # ARMv7M
Tested-by: Simon Horman <horms+renesas@verge.net.au> # Shmobile
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/arm/mm/proc-arm740.S b/arch/arm/mm/proc-arm740.S
index 9b0ae90cbf17..ac1ea6b3bce4 100644
--- a/arch/arm/mm/proc-arm740.S
+++ b/arch/arm/mm/proc-arm740.S
@@ -32,7 +32,7 @@ ENTRY(cpu_arm740_proc_init)
 ENTRY(cpu_arm740_do_idle)
 ENTRY(cpu_arm740_dcache_clean_area)
 ENTRY(cpu_arm740_switch_mm)
-        mov     pc, lr
+        ret     lr
 
 /*
  * cpu_arm740_proc_fin()
@@ -42,7 +42,7 @@ ENTRY(cpu_arm740_proc_fin)
         bic     r0, r0, #0x3f000000             @ bank/f/lock/s
         bic     r0, r0, #0x0000000c             @ w-buffer/cache
         mcr     p15, 0, r0, c1, c0, 0           @ disable caches
-        mov     pc, lr
+        ret     lr
 
 /*
  * cpu_arm740_reset(loc)
@@ -56,7 +56,7 @@ ENTRY(cpu_arm740_reset)
         mrc     p15, 0, ip, c1, c0, 0           @ get ctrl register
         bic     ip, ip, #0x0000000c             @ ............wc..
         mcr     p15, 0, ip, c1, c0, 0           @ ctrl register
-        mov     pc, r0
+        ret     r0
 ENDPROC(cpu_arm740_reset)
         .popsection
 
@@ -115,7 +115,7 @@ __arm740_setup:
                                                 @ need some benchmark
         orr     r0, r0, #0x0000000d             @ MPU/Cache/WB
 
-        mov     pc, lr
+        ret     lr
 
         .size   __arm740_setup, . - __arm740_setup