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/kernel/head.S

@@ -140,7 +140,7 @@ ENTRY(stext)
 	mov	r8, r4				@ set TTBR1 to swapper_pg_dir
  ARM(	add	pc, r10, #PROCINFO_INITFUNC	)
  THUMB(	add	r12, r10, #PROCINFO_INITFUNC	)
- THUMB(	mov	pc, r12				)
+ THUMB(	ret	r12				)
 1:	b	__enable_mmu
 ENDPROC(stext)
 	.ltorg
@@ -335,7 +335,7 @@ __create_page_tables:
 	sub	r4, r4, #0x1000		@ point to the PGD table
 	mov	r4, r4, lsr #ARCH_PGD_SHIFT
 #endif
-	mov	pc, lr
+	ret	lr
 ENDPROC(__create_page_tables)
 	.ltorg
 	.align
@@ -383,7 +383,7 @@ ENTRY(secondary_startup)
  ARM(	add	pc, r10, #PROCINFO_INITFUNC	) @ initialise processor
 						  @ (return control reg)
  THUMB(	add	r12, r10, #PROCINFO_INITFUNC	)
- THUMB(	mov	pc, r12				)
+ THUMB(	ret	r12				)
 ENDPROC(secondary_startup)
 
 	/*
@@ -468,7 +468,7 @@ ENTRY(__turn_mmu_on)
 	instr_sync
 	mov	r3, r3
 	mov	r3, r13
-	mov	pc, r3
+	ret	r3
 __turn_mmu_on_end:
 ENDPROC(__turn_mmu_on)
 	.popsection
@@ -487,7 +487,7 @@ __fixup_smp:
 	orr	r4, r4, #0x0000b000
 	orr	r4, r4, #0x00000020	@ val 0x4100b020
 	teq	r3, r4			@ ARM 11MPCore?
-	moveq	pc, lr			@ yes, assume SMP
+	reteq	lr			@ yes, assume SMP
 
 	mrc	p15, 0, r0, c0, c0, 5	@ read MPIDR
 	and	r0, r0, #0xc0000000	@ multiprocessing extensions and
@@ -500,7 +500,7 @@ __fixup_smp:
 	orr	r4, r4, #0x0000c000
 	orr	r4, r4, #0x00000090
 	teq	r3, r4			@ Check for ARM Cortex-A9
-	movne	pc, lr			@ Not ARM Cortex-A9,
+	retne	lr			@ Not ARM Cortex-A9,
 
 	@ If a future SoC *does* use 0x0 as the PERIPH_BASE, then the
 	@ below address check will need to be #ifdef'd or equivalent
@@ -512,7 +512,7 @@ __fixup_smp:
 ARM_BE8(rev	r0, r0)			@ byteswap if big endian
 	and	r0, r0, #0x3		@ number of CPUs
 	teq	r0, #0x0		@ is 1?
-	movne	pc, lr
+	retne	lr
 
 __fixup_smp_on_up:
 	adr	r0, 1f
@@ -539,7 +539,7 @@ smp_on_up:
 	.text
 __do_fixup_smp_on_up:
 	cmp	r4, r5
-	movhs	pc, lr
+	reths	lr
 	ldmia	r4!, {r0, r6}
  ARM(	str	r6, [r0, r3]	)
  THUMB(	add	r0, r0, r3	)
@@ -672,7 +672,7 @@ ARM_BE8(rev16	ip, ip)
 2:	cmp	r4, r5
 	ldrcc	r7, [r4], #4	@ use branch for delay slot
 	bcc	1b
-	mov	pc, lr
+	ret	lr
 #endif
 ENDPROC(__fixup_a_pv_table)