linux-kernel - [PATCH] ARM: armv6 & armv7 no need update SCTLR for alignment

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Message-ID: <BB7C62C2B0732E4DA93834A501E846456C8F1D93@szxema505-mbx.china.huawei.com>
Date:	Thu, 24 Apr 2014 01:32:32 +0000
From:	Wuqixuan <wuqixuan@...wei.com>
To:	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Lizefan <lizefan@...wei.com>, qixuan wu <wuqixuan@...il.com>
Subject: [PATCH] ARM: armv6 & armv7 no need update SCTLR for alignment

Now in the code, when interrupt and exception disturbs the user-space, always
update SCTLR with cr_alignment. In our ARMv7 Cortex A15 SOC, the statements  
bracketed by CONFIG_ALIGNMENT_TRAP need about 100 cycles. it impacts our 
high realtime interrupt requirement scenario. Considering in ARMv6 and ARMv7 
versions, cr_alignment and cr_no_alignment are always same without A bit, 
they are initialized by clearing A bit in alignment_init. So there is no 
need to update SCTLR if interrupt and exception disturbs the user-space
in vector_swi function or alignment_trap macro, in the ARMv6 and ARMv7 chip. 
The patch has already verified in our ARMv7 Cortex A15 SOC. 
Signed-off-by: Wuqixuan <wuqixuan@...wei.com>
---
 arch/arm/kernel/entry-common.S |    4 ++--
 arch/arm/kernel/entry-header.S |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index a2dcafd..4b7686a 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -366,7 +366,7 @@ ENTRY(vector_swi)
 #endif
  zero_fp
 
-#ifdef CONFIG_ALIGNMENT_TRAP
+#if defined(CONFIG_ALIGNMENT_TRAP) && !(__LINUX_ARM_ARCH__ >= 6)
  ldr ip, __cr_alignment
  ldr ip, [ip]
  mcr p15, 0, ip, c1, c0  @ update control register
@@ -490,7 +490,7 @@ __sys_trace_return:
  b ret_slow_syscall
 
  .align 5
-#ifdef CONFIG_ALIGNMENT_TRAP
+#if defined(CONFIG_ALIGNMENT_TRAP) && !(__LINUX_ARM_ARCH__ >= 6)
  .type __cr_alignment, #object
 __cr_alignment:
  .word cr_alignment
diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index 1420725..5eb9e59 100644
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -38,7 +38,7 @@
  .endm
 
  .macro alignment_trap, rtemp
-#ifdef CONFIG_ALIGNMENT_TRAP
+#if defined(CONFIG_ALIGNMENT_TRAP) && !(__LINUX_ARM_ARCH__ >= 6)
  ldr \rtemp, .LCcralign
  ldr \rtemp, [\rtemp]
  mcr p15, 0, \rtemp, c1, c0
-- 
1.7.6--
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