From: Stephen Boyd <sboyd@codeaurora.org> To: Greg KH <greg@kroah.com> Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Arnd Bergmann <arnd@arndb.de>, Daniel Walker <dwalker@codeaurora.org> Subject: [PATCHv2 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Date: Thu, 3 Feb 2011 15:48:34 -0800 [thread overview] Message-ID: <1296776916-21018-2-git-send-email-sboyd@codeaurora.org> (raw) In-Reply-To: <1296776916-21018-1-git-send-email-sboyd@codeaurora.org> Without marking the asm __dcc_getstatus() volatile my compiler decides it can cache the value of __ret in a register and then check the value of it continually in hvc_dcc_put_chars() (I had to replace get_wait/put_wait with 1 and fixup the branch otherwise my disassembler barfed on __dcc_(get|put)char). 00000000 <hvc_dcc_put_chars>: 0: ee103e11 mrc 14, 0, r3, cr0, cr1, {0} 4: e3a0c000 mov ip, #0 ; 0x0 8: e2033202 and r3, r3, #536870912 ; 0x20000000 c: ea000006 b 2c <hvc_dcc_put_chars+0x2c> 10: e3530000 cmp r3, #0 ; 0x0 14: 1afffffd bne 10 <hvc_dcc_put_chars+0x10> 18: e7d1000c ldrb r0, [r1, ip] 1c: ee10fe11 mrc 14, 0, pc, cr0, cr1, {0} 20: 2afffffd bcs 1c <hvc_dcc_put_chars+0x1c> 24: ee000e15 mcr 14, 0, r0, cr0, cr5, {0} 28: e28cc001 add ip, ip, #1 ; 0x1 2c: e15c0002 cmp ip, r2 30: bafffff6 blt 10 <hvc_dcc_put_chars+0x10> 34: e1a00002 mov r0, r2 38: e12fff1e bx lr As you can see, the value of the mrc is checked against DCC_STATUS_TX (bit 29) and then stored in r3 for later use. Marking the asm volatile produces the following: 00000000 <hvc_dcc_put_chars>: 0: e3a03000 mov r3, #0 ; 0x0 4: ea000007 b 28 <hvc_dcc_put_chars+0x28> 8: ee100e11 mrc 14, 0, r0, cr0, cr1, {0} c: e3100202 tst r0, #536870912 ; 0x20000000 10: 1afffffc bne 8 <hvc_dcc_put_chars+0x8> 14: e7d10003 ldrb r0, [r1, r3] 18: ee10fe11 mrc 14, 0, pc, cr0, cr1, {0} 1c: 2afffffd bcs 18 <hvc_dcc_put_chars+0x18> 20: ee000e15 mcr 14, 0, r0, cr0, cr5, {0} 24: e2833001 add r3, r3, #1 ; 0x1 28: e1530002 cmp r3, r2 2c: bafffff5 blt 8 <hvc_dcc_put_chars+0x8> 30: e1a00002 mov r0, r2 34: e12fff1e bx lr which looks better and actually works. Mark all the inline assembly in this file as volatile since we don't want the compiler to optimize away these statements or move them around in any way. Acked-by: Tony Lindgren <tony@atomide.com> Cc: Arnd Bergmann <arnd@arndb.de> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org> Cc: Daniel Walker <dwalker@codeaurora.org> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> --- drivers/tty/hvc/hvc_dcc.c | 11 +++++------ 1 files changed, 5 insertions(+), 6 deletions(-) diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c index 6470f63..155ec10 100644 --- a/drivers/tty/hvc/hvc_dcc.c +++ b/drivers/tty/hvc/hvc_dcc.c @@ -33,8 +33,7 @@ static inline u32 __dcc_getstatus(void) { u32 __ret; - - asm("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg" + asm volatile("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg" : "=r" (__ret) : : "cc"); return __ret; @@ -46,7 +45,7 @@ static inline char __dcc_getchar(void) { char __c; - asm("get_wait: mrc p14, 0, pc, c0, c1, 0 \n\ + asm volatile("get_wait: mrc p14, 0, pc, c0, c1, 0 \n\ bne get_wait \n\ mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" : "=r" (__c) : : "cc"); @@ -58,7 +57,7 @@ static inline char __dcc_getchar(void) { char __c; - asm("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" + asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" : "=r" (__c)); return __c; @@ -68,7 +67,7 @@ static inline char __dcc_getchar(void) #if defined(CONFIG_CPU_V7) static inline void __dcc_putchar(char c) { - asm("put_wait: mrc p14, 0, pc, c0, c1, 0 \n\ + asm volatile("put_wait: mrc p14, 0, pc, c0, c1, 0 \n\ bcs put_wait \n\ mcr p14, 0, %0, c0, c5, 0 " : : "r" (c) : "cc"); @@ -76,7 +75,7 @@ static inline void __dcc_putchar(char c) #else static inline void __dcc_putchar(char c) { - asm("mcr p14, 0, %0, c0, c5, 0 @ write a char" + asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char" : /* no output register */ : "r" (c)); } -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
WARNING: multiple messages have this Message-ID (diff)
From: sboyd@codeaurora.org (Stephen Boyd) To: linux-arm-kernel@lists.infradead.org Subject: [PATCHv2 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Date: Thu, 3 Feb 2011 15:48:34 -0800 [thread overview] Message-ID: <1296776916-21018-2-git-send-email-sboyd@codeaurora.org> (raw) In-Reply-To: <1296776916-21018-1-git-send-email-sboyd@codeaurora.org> Without marking the asm __dcc_getstatus() volatile my compiler decides it can cache the value of __ret in a register and then check the value of it continually in hvc_dcc_put_chars() (I had to replace get_wait/put_wait with 1 and fixup the branch otherwise my disassembler barfed on __dcc_(get|put)char). 00000000 <hvc_dcc_put_chars>: 0: ee103e11 mrc 14, 0, r3, cr0, cr1, {0} 4: e3a0c000 mov ip, #0 ; 0x0 8: e2033202 and r3, r3, #536870912 ; 0x20000000 c: ea000006 b 2c <hvc_dcc_put_chars+0x2c> 10: e3530000 cmp r3, #0 ; 0x0 14: 1afffffd bne 10 <hvc_dcc_put_chars+0x10> 18: e7d1000c ldrb r0, [r1, ip] 1c: ee10fe11 mrc 14, 0, pc, cr0, cr1, {0} 20: 2afffffd bcs 1c <hvc_dcc_put_chars+0x1c> 24: ee000e15 mcr 14, 0, r0, cr0, cr5, {0} 28: e28cc001 add ip, ip, #1 ; 0x1 2c: e15c0002 cmp ip, r2 30: bafffff6 blt 10 <hvc_dcc_put_chars+0x10> 34: e1a00002 mov r0, r2 38: e12fff1e bx lr As you can see, the value of the mrc is checked against DCC_STATUS_TX (bit 29) and then stored in r3 for later use. Marking the asm volatile produces the following: 00000000 <hvc_dcc_put_chars>: 0: e3a03000 mov r3, #0 ; 0x0 4: ea000007 b 28 <hvc_dcc_put_chars+0x28> 8: ee100e11 mrc 14, 0, r0, cr0, cr1, {0} c: e3100202 tst r0, #536870912 ; 0x20000000 10: 1afffffc bne 8 <hvc_dcc_put_chars+0x8> 14: e7d10003 ldrb r0, [r1, r3] 18: ee10fe11 mrc 14, 0, pc, cr0, cr1, {0} 1c: 2afffffd bcs 18 <hvc_dcc_put_chars+0x18> 20: ee000e15 mcr 14, 0, r0, cr0, cr5, {0} 24: e2833001 add r3, r3, #1 ; 0x1 28: e1530002 cmp r3, r2 2c: bafffff5 blt 8 <hvc_dcc_put_chars+0x8> 30: e1a00002 mov r0, r2 34: e12fff1e bx lr which looks better and actually works. Mark all the inline assembly in this file as volatile since we don't want the compiler to optimize away these statements or move them around in any way. Acked-by: Tony Lindgren <tony@atomide.com> Cc: Arnd Bergmann <arnd@arndb.de> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org> Cc: Daniel Walker <dwalker@codeaurora.org> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> --- drivers/tty/hvc/hvc_dcc.c | 11 +++++------ 1 files changed, 5 insertions(+), 6 deletions(-) diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c index 6470f63..155ec10 100644 --- a/drivers/tty/hvc/hvc_dcc.c +++ b/drivers/tty/hvc/hvc_dcc.c @@ -33,8 +33,7 @@ static inline u32 __dcc_getstatus(void) { u32 __ret; - - asm("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg" + asm volatile("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg" : "=r" (__ret) : : "cc"); return __ret; @@ -46,7 +45,7 @@ static inline char __dcc_getchar(void) { char __c; - asm("get_wait: mrc p14, 0, pc, c0, c1, 0 \n\ + asm volatile("get_wait: mrc p14, 0, pc, c0, c1, 0 \n\ bne get_wait \n\ mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" : "=r" (__c) : : "cc"); @@ -58,7 +57,7 @@ static inline char __dcc_getchar(void) { char __c; - asm("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" + asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" : "=r" (__c)); return __c; @@ -68,7 +67,7 @@ static inline char __dcc_getchar(void) #if defined(CONFIG_CPU_V7) static inline void __dcc_putchar(char c) { - asm("put_wait: mrc p14, 0, pc, c0, c1, 0 \n\ + asm volatile("put_wait: mrc p14, 0, pc, c0, c1, 0 \n\ bcs put_wait \n\ mcr p14, 0, %0, c0, c5, 0 " : : "r" (c) : "cc"); @@ -76,7 +75,7 @@ static inline void __dcc_putchar(char c) #else static inline void __dcc_putchar(char c) { - asm("mcr p14, 0, %0, c0, c5, 0 @ write a char" + asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char" : /* no output register */ : "r" (c)); } -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
next prev parent reply other threads:[~2011-02-03 23:48 UTC|newest] Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-11-30 19:25 [PATCH] drivers: char: hvc: add arm JTAG DCC console support Daniel Walker 2010-11-30 19:25 ` Daniel Walker 2010-11-30 19:57 ` Nicolas Pitre 2010-11-30 19:57 ` Nicolas Pitre 2010-11-30 21:17 ` Arnd Bergmann 2010-11-30 21:17 ` Arnd Bergmann 2010-12-01 5:30 ` Stephen Boyd 2010-12-01 5:30 ` Stephen Boyd 2010-12-01 18:54 ` Daniel Walker 2010-12-01 18:54 ` Daniel Walker 2010-12-01 19:28 ` Greg KH 2010-12-01 19:28 ` Greg KH 2010-12-18 5:16 ` [PATCH] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd 2010-12-18 5:16 ` Stephen Boyd 2010-12-20 17:51 ` Daniel Walker 2010-12-20 17:51 ` Daniel Walker 2010-12-20 18:39 ` Stephen Boyd 2010-12-20 18:39 ` Stephen Boyd 2010-12-20 18:46 ` Nicolas Pitre 2010-12-20 18:46 ` Nicolas Pitre 2010-12-20 20:08 ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd 2010-12-20 20:08 ` Stephen Boyd 2010-12-20 20:08 ` [PATCH 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd 2010-12-20 20:08 ` Stephen Boyd 2010-12-20 21:39 ` Nicolas Pitre 2010-12-20 21:39 ` Nicolas Pitre 2011-01-02 9:00 ` Pavel Machek 2011-01-02 9:00 ` Pavel Machek 2011-01-02 18:49 ` David Brown 2011-01-02 18:49 ` David Brown 2011-01-03 5:50 ` Pavel Machek 2011-01-03 5:50 ` Pavel Machek 2011-01-04 18:49 ` Tony Lindgren 2011-01-04 18:49 ` Tony Lindgren 2010-12-20 21:49 ` Arnaud Lacombe 2010-12-20 21:49 ` Arnaud Lacombe 2010-12-20 21:52 ` Stephen Boyd 2010-12-20 21:52 ` Stephen Boyd 2010-12-20 22:10 ` Nicolas Pitre 2010-12-20 22:10 ` Nicolas Pitre 2010-12-20 20:08 ` [PATCH 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd 2010-12-20 20:08 ` Stephen Boyd 2010-12-20 20:08 ` [PATCH 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd 2010-12-20 20:08 ` Stephen Boyd 2010-12-20 21:44 ` Nicolas Pitre 2010-12-20 21:44 ` Nicolas Pitre 2011-01-04 18:52 ` Tony Lindgren 2011-01-04 18:52 ` Tony Lindgren 2011-01-06 1:49 ` [PATCH 0/3] hvc_dcc cleanups and fixes Stephen Boyd 2011-01-06 1:49 ` Stephen Boyd 2011-01-06 3:20 ` Greg KH 2011-01-06 3:20 ` Greg KH 2011-02-03 22:17 ` Greg KH 2011-02-03 22:17 ` Greg KH 2011-02-03 22:17 ` Greg KH 2011-02-03 23:19 ` Stephen Boyd 2011-02-03 23:19 ` Stephen Boyd 2011-02-03 23:30 ` Greg KH 2011-02-03 23:30 ` Greg KH 2011-02-03 23:48 ` [PATCHv2 " Stephen Boyd 2011-02-03 23:48 ` Stephen Boyd 2011-02-03 23:48 ` Stephen Boyd [this message] 2011-02-03 23:48 ` [PATCHv2 1/3] hvc_dcc: Fix bad code generation by marking assembly volatile Stephen Boyd 2011-02-03 23:48 ` [PATCHv2 2/3] hvc_dcc: Simplify put_chars()/get_chars() loops Stephen Boyd 2011-02-03 23:48 ` Stephen Boyd 2011-02-03 23:48 ` [PATCHv2 3/3] hvc_dcc: Simplify assembly for v6 and v7 ARM Stephen Boyd 2011-02-03 23:48 ` Stephen Boyd 2010-12-01 20:20 ` [PATCH] drivers: char: hvc: add arm JTAG DCC console support Stephen Boyd 2010-12-01 20:20 ` Stephen Boyd 2010-12-07 19:10 ` Stephen Boyd 2010-12-07 19:10 ` Stephen Boyd 2011-01-14 19:19 ` Tony Lindgren 2011-01-14 19:19 ` Tony Lindgren 2011-01-14 23:49 ` Stephen Boyd 2011-01-14 23:49 ` Stephen Boyd 2011-04-07 18:39 ` RONETIX - Asen Dimov 2011-04-07 18:39 ` RONETIX - Asen Dimov 2011-04-07 18:57 ` Mike Frysinger 2011-04-07 18:57 ` Mike Frysinger
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