[ARM] Optimise kernel->userspace exit code a little.

This improves interrupts and exceptions returning to user space
by a few of cycles.  We change the requirements for
*_restore_user_regs slightly so we can remove a few instructions.
We also re-shuffle the code to handle pending work.

arch/arm/kernel/entry-armv.S

@@ -725,7 +725,7 @@ __dabt_svc:	sub	sp, sp, #S_FRAME_SIZE
 		msr	cpsr_c, r9
 		mov	r2, sp
 		bl	do_DataAbort
-		set_cpsr_c r0, #PSR_I_BIT | MODE_SVC
+		disable_irq r0
 		ldr	r0, [sp, #S_PSR]
 		msr	spsr, r0
 		ldmia	sp, {r0 - pc}^			@ load r0 - pc, cpsr
@@ -776,9 +776,9 @@ svc_preempt:	teq	r9, #0				@ was preempt count = 0
 		movne	pc, lr
 		mov	r7, #PREEMPT_ACTIVE
 		str	r7, [r8, #TI_PREEMPT]		@ set PREEMPT_ACTIVE
-1:		set_cpsr_c r2, #MODE_SVC		@ enable IRQs
+1:		enable_irq r2				@ enable IRQs
 		bl	schedule
-		set_cpsr_c r0, #PSR_I_BIT | MODE_SVC	@ disable IRQs
+		disable_irq r0				@ disable IRQs
 		ldr	r0, [r8, #TI_FLAGS]		@ get new tasks TI_FLAGS
 		tst	r0, #_TIF_NEED_RESCHED
 		beq	preempt_return			@ go again
@@ -801,7 +801,7 @@ __und_svc:	sub	sp, sp, #S_FRAME_SIZE
 		mov	r0, sp				@ struct pt_regs *regs
 		bl	do_undefinstr
 
-1:		set_cpsr_c r0, #PSR_I_BIT | MODE_SVC
+1:		disable_irq r0
 		ldr	lr, [sp, #S_PSR]		@ Get SVC cpsr
 		msr	spsr, lr
 		ldmia	sp, {r0 - pc}^			@ Restore SVC registers
@@ -822,7 +822,7 @@ __pabt_svc:	sub	sp, sp, #S_FRAME_SIZE
 		mov	r0, r2				@ address (pc)
 		mov	r1, sp				@ regs
 		bl	do_PrefetchAbort		@ call abort handler
-		set_cpsr_c r0, #PSR_I_BIT | MODE_SVC
+		disable_irq r0
 		ldr	r0, [sp, #S_PSR]
 		msr	spsr, r0
 		ldmia	sp, {r0 - pc}^			@ load r0 - pc, cpsr
@@ -861,7 +861,7 @@ __dabt_usr:	sub	sp, sp, #S_FRAME_SIZE		@ Allocate frame size in one go
 #else
 		bl	CPU_ABORT_HANDLER
 #endif
-		set_cpsr_c r2, #MODE_SVC		@ Enable interrupts
+		enable_irq r2				@ Enable interrupts
 		mov	r2, sp
 		adrsvc	al, lr, ret_from_exception
 		b	do_DataAbort
@@ -916,7 +916,7 @@ __und_usr:	sub	sp, sp, #S_FRAME_SIZE		@ Allocate frame size in one go
 		adrsvc	al, r9, ret_from_exception	@ r9  = normal FP return
 		adrsvc	al, lr, fpundefinstr		@ lr  = undefined instr return
 
-call_fpe:	set_cpsr_c r0, #MODE_SVC		@ Enable interrupts
+call_fpe:	enable_irq r0				@ Enable interrupts
 		get_thread_info r10			@ get current thread
 		ldr	r4, [r10, #TI_TASK]		@ get current task
 		mov	r8, #1
@@ -939,7 +939,7 @@ __pabt_usr:	sub	sp, sp, #S_FRAME_SIZE		@ Allocate frame size in one go
 		stmdb	r8, {sp, lr}^			@ Save sp_usr lr_usr
 		alignment_trap r4, r7, __temp_abt
 		zero_fp
-		set_cpsr_c r0, #MODE_SVC		@ Enable interrupts
+		enable_irq r0				@ Enable interrupts
 		mov	r0, r5				@ address (pc)
 		mov	r1, sp				@ regs
 		bl	do_PrefetchAbort		@ call abort handler

arch/arm/kernel/entry-common.S

@@ -35,18 +35,27 @@ ENTRY(__do_softirq)
  * stack.
  */
 ret_fast_syscall:
-	set_cpsr_c r1, #PSR_I_BIT | MODE_SVC	@ disable interrupts
+	disable_irq r1				@ disable interrupts
 	ldr	r1, [tsk, #TI_FLAGS]
 	tst	r1, #_TIF_WORK_MASK
-	bne	ret_fast_work
+	bne	fast_work_pending
 	fast_restore_user_regs
 
 /*
  * Ok, we need to do extra processing, enter the slow path.
  */
-ret_fast_work:
+fast_work_pending:
 	str	r0, [sp, #S_R0+S_OFF]!		@ returned r0
-	b	work_pending
+work_pending:
+	tst	r1, #_TIF_NEED_RESCHED
+	bne	work_resched
+	tst	r1, #_TIF_NOTIFY_RESUME | _TIF_SIGPENDING
+	beq	no_work_pending
+	mov	r0, sp				@ 'regs'
+	mov	r2, why				@ 'syscall'
+	bl	do_notify_resume
+	disable_irq r1				@ disable interrupts
+	b	no_work_pending
 
 work_resched:
 	bl	schedule
@@ -55,22 +64,12 @@ work_resched:
  */
 ENTRY(ret_to_user)
 ret_slow_syscall:
-	set_cpsr_c r1, #PSR_I_BIT | MODE_SVC	@ disable interrupts
+	disable_irq r1				@ disable interrupts
 	ldr	r1, [tsk, #TI_FLAGS]
 	tst	r1, #_TIF_WORK_MASK
-	beq	no_work_pending
-work_pending:
-	tst	r1, #_TIF_NEED_RESCHED
-	bne	work_resched
-	tst	r1, #_TIF_NOTIFY_RESUME | _TIF_SIGPENDING
-	blne	__do_notify_resume
+	bne	work_pending
 no_work_pending:
-	restore_user_regs
-
-__do_notify_resume:
-	mov	r0, sp				@ 'regs'
-	mov	r2, why				@ 'syscall'
-	b	do_notify_resume		@ note the bl above sets lr
+	slow_restore_user_regs
 
 /*
  * This is how we return from a fork.
@@ -80,9 +79,9 @@ ENTRY(ret_from_fork)
 	bl	schedule_tail
 #endif
 	get_thread_info tsk
-	ldr	ip, [tsk, #TI_FLAGS]		@ check for syscall tracing
+	ldr	r1, [tsk, #TI_FLAGS]		@ check for syscall tracing
 	mov	why, #1
-	tst	ip, #_TIF_SYSCALL_TRACE		@ are we tracing syscalls?
+	tst	r1, #_TIF_SYSCALL_TRACE		@ are we tracing syscalls?
 	beq	ret_slow_syscall
 	mov	r1, sp
 	mov	r0, #1				@ trace exit [IP = 1]
@@ -134,7 +133,7 @@ ENTRY(vector_swi)
 	ldr	ip, [ip]
 	mcr	p15, 0, ip, c1, c0		@ update control register
 #endif
-	enable_irqs ip
+	enable_irq ip
 
 	str	r4, [sp, #-S_OFF]!		@ push fifth arg
 

arch/arm/kernel/entry-header.S

@@ -69,6 +69,25 @@
 #define S_OFF		8
 
 #ifdef CONFIG_CPU_32
+
+	.macro	set_cpsr_c, reg, mode
+#if 1
+	/* broken binutils */
+	mov	\reg, \mode
+	msr	cpsr_c, \reg
+#else
+	msr	cpsr_c, \mode
+#endif
+	.endm
+
+	.macro	disable_irq, temp
+	set_cpsr_c \temp, #PSR_I_BIT | MODE_SVC
+	.endm
+
+	.macro	enable_irq, temp
+	set_cpsr_c \temp, #MODE_SVC
+	.endm
+
 	.macro	save_user_regs
 	sub	sp, sp, #S_FRAME_SIZE
 	stmia	sp, {r0 - r12}			@ Calling r0 - r12
@@ -81,20 +100,20 @@
 	.endm
 
 	.macro	restore_user_regs
-		ldr	r0, [sp, #S_PSR]		@ Get calling cpsr
-		mov	ip, #PSR_I_BIT | MODE_SVC
-		msr	cpsr_c, ip			@ disable IRQs
-		msr	spsr, r0			@ save in spsr_svc
-		ldr	lr, [sp, #S_PC]			@ Get PC
-		ldmia	sp, {r0 - lr}^			@ Get calling r0 - lr
+	ldr	r1, [sp, #S_PSR]		@ Get calling cpsr
+	disable_irq ip				@ disable IRQs
+	ldr	lr, [sp, #S_PC]!		@ Get PC
+	msr	spsr, r1			@ save in spsr_svc
+	ldmdb	sp, {r0 - lr}^			@ Get calling r0 - lr
 	mov	r0, r0
-		add	sp, sp, #S_FRAME_SIZE
+	add	sp, sp, #S_FRAME_SIZE - S_PC
 	movs	pc, lr				@ return & move spsr_svc into cpsr
 	.endm
 
+/*
+ * Must be called with IRQs already disabled.
+ */
 	.macro	fast_restore_user_regs
-		mov	ip, #PSR_I_BIT | MODE_SVC
-		msr	cpsr_c, ip			@ disable IRQs
 	ldr	r1, [sp, #S_OFF + S_PSR]	@ get calling cpsr
 	ldr	lr, [sp, #S_OFF + S_PC]!	@ get pc
 	msr	spsr, r1			@ save in spsr_svc
@@ -104,12 +123,20 @@
 	movs	pc, lr				@ return & move spsr_svc into cpsr
 	.endm
 
-		.macro	mask_pc, rd, rm
+/*
+ * Must be called with IRQs already disabled.
+ */
+	.macro	slow_restore_user_regs
+	ldr	r1, [sp, #S_PSR]		@ get calling cpsr
+	ldr	lr, [sp, #S_PC]!		@ get pc
+	msr	spsr, r1			@ save in spsr_svc
+	ldmdb	sp, {r0 - lr}^			@ get calling r1 - lr
+	mov	r0, r0
+	add	sp, sp, #S_FRAME_SIZE - S_PC
+	movs	pc, lr				@ return & move spsr_svc into cpsr
 	.endm
 
-		.macro	enable_irqs, temp
-		mov	\temp, #MODE_SVC
-		msr	cpsr_c, \temp
+	.macro	mask_pc, rd, rm
 	.endm
 
 	.macro	get_thread_info, rd
@@ -117,7 +144,7 @@
 	mov	\rd, \rd, lsl #13
 	.endm
 
-		/*
+/*
  * Like adr, but force SVC mode (if required)
  */
 	.macro	adrsvc, cond, reg, label
@@ -215,13 +242,3 @@ tsk	.req	r9		@ current thread_info
 	ldr	scno, [lr, #-4]		@ get SWI instruction
 #endif
 	.endm
-
-	.macro	set_cpsr_c, reg, mode
-#if 1
-	mov	\reg, \mode
-	msr	cpsr_c, \reg
-#else
-	msr	cpsr_c, \mode
-#endif
-	.endm
-