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arch/sparc: Introduce cmpxchg_u8 SPARC 

SPARC supports 32 bit and 64 bit cmpxchg right now. Add support
for 8 bit (1 byte) cmpxchg. This is required to support queued
rwlocks feature  which uses 1 byte cmpxchg.

The function __cmpxchg_u8 here uses the 4 byte cas instruction with a
byte manipulation to achieve 1 byte cmpxchg.

Signed-off-by: Babu Moger <babu.moger@oracle.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Reviewed-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Reviewed-by: Jane Chu <jane.chu@oracle.com>
Reviewed-by: Vijay Kumar <vijay.ac.kumar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Babu Moger 2017-05-24 17:55:12 -06:00 committed by David S. Miller
parent 97d9f96916
commit a12ee23493
1 changed files with 29 additions and 0 deletions
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29
arch/sparc/include/asm/cmpxchg_64.h
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@ -87,6 +87,33 @@ __cmpxchg_u64(volatile long *m, unsigned long old, unsigned long new)
return new;
}
/*
* Use 4 byte cas instruction to achieve 1 byte cmpxchg. Main logic
* here is to get the bit shift of the byte we are interested in.
* The XOR is handy for reversing the bits for big-endian byte order
*/
static inline unsigned long
__cmpxchg_u8(volatile unsigned char *m, unsigned char old, unsigned char new)
{
unsigned long maddr = (unsigned long)m;
int bit_shift = (((unsigned long)m & 3) ^ 3) << 3;
unsigned int mask = 0xff << bit_shift;
unsigned int *ptr = (unsigned int *) (maddr & ~3);
unsigned int old32, new32, load;
unsigned int load32 = *ptr;
do {
new32 = (load32 & ~mask) | (new << bit_shift);
old32 = (load32 & ~mask) | (old << bit_shift);
load32 = __cmpxchg_u32(ptr, old32, new32);
if (load32 == old32)
return old;
load = (load32 & mask) >> bit_shift;
} while (load == old);
return load;
}
/* This function doesn't exist, so you'll get a linker error
if something tries to do an invalid cmpxchg(). */
void __cmpxchg_called_with_bad_pointer(void);
@ -95,6 +122,8 @@ static inline unsigned long
__cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
{
switch (size) {
case 1:
return __cmpxchg_u8(ptr, old, new);
case 4:
return __cmpxchg_u32(ptr, old, new);
case 8: