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authorStephen Boyd <sboyd@codeaurora.org>2011-02-03 18:48:34 -0500
committerGreg Kroah-Hartman <gregkh@suse.de>2011-02-03 19:05:43 -0500
commita99632014631409483a481a6a0d77d09ded47239 (patch)
treee2997ea820ece1a9765f2b64ae36e55830379ada /drivers/tty/hvc
parent380042f2db653b324ae756d102d872c1ecd412c5 (diff)
hvc_dcc: Fix bad code generation by marking assembly volatile
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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers/tty/hvc')
-rw-r--r--drivers/tty/hvc/hvc_dcc.c11
1 files changed, 5 insertions, 6 deletions
diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c
index 6470f63deb4b..155ec105e1c8 100644
--- a/drivers/tty/hvc/hvc_dcc.c
+++ b/drivers/tty/hvc/hvc_dcc.c
@@ -33,8 +33,7 @@
33static inline u32 __dcc_getstatus(void) 33static inline u32 __dcc_getstatus(void)
34{ 34{
35 u32 __ret; 35 u32 __ret;
36 36 asm volatile("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg"
37 asm("mrc p14, 0, %0, c0, c1, 0 @ read comms ctrl reg"
38 : "=r" (__ret) : : "cc"); 37 : "=r" (__ret) : : "cc");
39 38
40 return __ret; 39 return __ret;
@@ -46,7 +45,7 @@ static inline char __dcc_getchar(void)
46{ 45{
47 char __c; 46 char __c;
48 47
49 asm("get_wait: mrc p14, 0, pc, c0, c1, 0 \n\ 48 asm volatile("get_wait: mrc p14, 0, pc, c0, c1, 0 \n\
50 bne get_wait \n\ 49 bne get_wait \n\
51 mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" 50 mrc p14, 0, %0, c0, c5, 0 @ read comms data reg"
52 : "=r" (__c) : : "cc"); 51 : "=r" (__c) : : "cc");
@@ -58,7 +57,7 @@ static inline char __dcc_getchar(void)
58{ 57{
59 char __c; 58 char __c;
60 59
61 asm("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg" 60 asm volatile("mrc p14, 0, %0, c0, c5, 0 @ read comms data reg"
62 : "=r" (__c)); 61 : "=r" (__c));
63 62
64 return __c; 63 return __c;
@@ -68,7 +67,7 @@ static inline char __dcc_getchar(void)
68#if defined(CONFIG_CPU_V7) 67#if defined(CONFIG_CPU_V7)
69static inline void __dcc_putchar(char c) 68static inline void __dcc_putchar(char c)
70{ 69{
71 asm("put_wait: mrc p14, 0, pc, c0, c1, 0 \n\ 70 asm volatile("put_wait: mrc p14, 0, pc, c0, c1, 0 \n\
72 bcs put_wait \n\ 71 bcs put_wait \n\
73 mcr p14, 0, %0, c0, c5, 0 " 72 mcr p14, 0, %0, c0, c5, 0 "
74 : : "r" (c) : "cc"); 73 : : "r" (c) : "cc");
@@ -76,7 +75,7 @@ static inline void __dcc_putchar(char c)
76#else 75#else
77static inline void __dcc_putchar(char c) 76static inline void __dcc_putchar(char c)
78{ 77{
79 asm("mcr p14, 0, %0, c0, c5, 0 @ write a char" 78 asm volatile("mcr p14, 0, %0, c0, c5, 0 @ write a char"
80 : /* no output register */ 79 : /* no output register */
81 : "r" (c)); 80 : "r" (c));
82} 81}