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, 3 deletions

diff --git a/arch/arm/mm/tlb-fa.S b/arch/arm/mm/tlb-fa.S
index d3ddcf9a76ca..d2d9ecbe0aac 100644
--- a/arch/arm/mm/tlb-fa.S
+++ b/arch/arm/mm/tlb-fa.S
@@ -18,6 +18,7 @@
  */
 #include <linux/linkage.h>
 #include <linux/init.h>
+#include <asm/assembler.h>
 #include <asm/asm-offsets.h>
 #include <asm/tlbflush.h>
 #include "proc-macros.S"
@@ -37,7 +38,7 @@ ENTRY(fa_flush_user_tlb_range)
         vma_vm_mm ip, r2
         act_mm  r3                              @ get current->active_mm
         eors    r3, ip, r3                      @ == mm ?
-        movne   pc, lr                          @ no, we dont do anything
+        retne   lr                              @ no, we dont do anything
         mov     r3, #0
         mcr     p15, 0, r3, c7, c10, 4          @ drain WB
         bic     r0, r0, #0x0ff
@@ -47,7 +48,7 @@ ENTRY(fa_flush_user_tlb_range)
         cmp     r0, r1
         blo     1b
         mcr     p15, 0, r3, c7, c10, 4          @ data write barrier
-        mov     pc, lr
+        ret     lr
 
 
 ENTRY(fa_flush_kern_tlb_range)
@@ -61,7 +62,7 @@ ENTRY(fa_flush_kern_tlb_range)
         blo     1b
         mcr     p15, 0, r3, c7, c10, 4          @ data write barrier
         mcr     p15, 0, r3, c7, c5, 4           @ prefetch flush (isb)
-        mov     pc, lr
+        ret     lr
 
         __INITDATA