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>

arch/arm/mm/proc-v7.S

@@ -26,7 +26,7 @@
 #endif
 
 ENTRY(cpu_v7_proc_init)
-	mov	pc, lr
+	ret	lr
 ENDPROC(cpu_v7_proc_init)
 
 ENTRY(cpu_v7_proc_fin)
@@ -34,7 +34,7 @@ ENTRY(cpu_v7_proc_fin)
 	bic	r0, r0, #0x1000			@ ...i............
 	bic	r0, r0, #0x0006			@ .............ca.
 	mcr	p15, 0, r0, c1, c0, 0		@ disable caches
-	mov	pc, lr
+	ret	lr
 ENDPROC(cpu_v7_proc_fin)
 
 /*
@@ -71,20 +71,20 @@ ENDPROC(cpu_v7_reset)
 ENTRY(cpu_v7_do_idle)
 	dsb					@ WFI may enter a low-power mode
 	wfi
-	mov	pc, lr
+	ret	lr
 ENDPROC(cpu_v7_do_idle)
 
 ENTRY(cpu_v7_dcache_clean_area)
 	ALT_SMP(W(nop))			@ MP extensions imply L1 PTW
 	ALT_UP_B(1f)
-	mov	pc, lr
+	ret	lr
 1:	dcache_line_size r2, r3
 2:	mcr	p15, 0, r0, c7, c10, 1		@ clean D entry
 	add	r0, r0, r2
 	subs	r1, r1, r2
 	bhi	2b
 	dsb	ishst
-	mov	pc, lr
+	ret	lr
 ENDPROC(cpu_v7_dcache_clean_area)
 
 	string	cpu_v7_name, "ARMv7 Processor"
@@ -163,7 +163,7 @@ ENTRY(cpu_pj4b_do_idle)
 	dsb					@ WFI may enter a low-power mode
 	wfi
 	dsb					@barrier
-	mov	pc, lr
+	ret	lr
 ENDPROC(cpu_pj4b_do_idle)
 #else
 	globl_equ	cpu_pj4b_do_idle,  	cpu_v7_do_idle
@@ -407,7 +407,7 @@ __v7_setup:
 	bic	r0, r0, r5			@ clear bits them
 	orr	r0, r0, r6			@ set them
  THUMB(	orr	r0, r0, #1 << 30	)	@ Thumb exceptions
-	mov	pc, lr				@ return to head.S:__ret
+	ret	lr				@ return to head.S:__ret
 ENDPROC(__v7_setup)
 
 	.align	2