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Commit 195b58ad authored by Russell King's avatar Russell King
Browse files

ARM: Avoid writing to control register on every exception 



If we are not changing the control register value, avoid writing to it.
Writes to the control register can be very expensive, taking around a
hundred cycles or so.

Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 8b521cb2

arch/arm/kernel/entry-armv.S

+7 −3
Original line number Diff line number Diff line
@@ -321,6 +321,9 @@ ENDPROC(__pabt_svc) 
 ARM(	stmib	sp, {r1 - r12}	)

 THUMB(	stmia	sp, {r0 - r12}	)



 ATRAP(	mrc	p15, 0, r7, c1, c0, 0)

 ATRAP(	ldr	r8, .LCcralign)



	ldmia	r0, {r3 - r5}

	add	r0, sp, #S_PC		@ here for interlock avoidance

	mov	r6, #-1			@  ""  ""     ""        ""
@@ -328,6 +331,8 @@ ENDPROC(__pabt_svc) 
	str	r3, [sp]		@ save the "real" r0 copied

					@ from the exception stack



 ATRAP(	ldr	r8, [r8, #0])



	@

	@ We are now ready to fill in the remaining blanks on the stack:

	@
@@ -341,10 +346,9 @@ ENDPROC(__pabt_svc) 
 ARM(	stmdb	r0, {sp, lr}^			)

 THUMB(	store_user_sp_lr r0, r1, S_SP - S_PC	)



	@

	@ Enable the alignment trap while in kernel mode

	@

	alignment_trap r0, .LCcralign

 ATRAP(	teq	r8, r7)

 ATRAP( mcrne	p15, 0, r8, c1, c0, 0)



	@

	@ Clear FP to mark the first stack frame

arch/arm/kernel/entry-common.S

+1 −1
Original line number Diff line number Diff line
@@ -366,7 +366,7 @@ ENTRY(vector_swi) 
	str	r0, [sp, #S_OLD_R0]		@ Save OLD_R0

#endif

	zero_fp

	alignment_trap ip, __cr_alignment

	alignment_trap r10, ip, __cr_alignment

	enable_irq

	ct_user_exit

	get_thread_info tsk

arch/arm/kernel/entry-header.S

+12 −4
Original line number Diff line number Diff line
@@ -37,11 +37,19 @@ 
#endif

	.endm



	.macro	alignment_trap, rtemp, label

#ifdef CONFIG_ALIGNMENT_TRAP

	ldr	\rtemp, \label

	ldr	\rtemp, [\rtemp]

	mcr	p15, 0, \rtemp, c1, c0

#define ATRAP(x...) x

#else

#define ATRAP(x...)

#endif



	.macro	alignment_trap, rtmp1, rtmp2, label

#ifdef CONFIG_ALIGNMENT_TRAP

	mrc	p15, 0, \rtmp2, c1, c0, 0

	ldr	\rtmp1, \label

	ldr	\rtmp1, [\rtmp1]

	teq	\rtmp1, \rtmp2

	mcrne	p15, 0, \rtmp1, c1, c0, 0

#endif

	.endm