From a12ee2349312d7112b9b7c6ac2e70c5ec2ca334e Mon Sep 17 00:00:00 2001 From: Babu Moger Date: Wed, 24 May 2017 17:55:12 -0600 Subject: arch/sparc: Introduce cmpxchg_u8 SPARC MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Håkon Bugge Reviewed-by: Steve Sistare Reviewed-by: Shannon Nelson Reviewed-by: Jane Chu Reviewed-by: Vijay Kumar Signed-off-by: David S. Miller --- arch/sparc/include/asm/cmpxchg_64.h | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) (limited to 'arch/sparc') diff --git a/arch/sparc/include/asm/cmpxchg_64.h b/arch/sparc/include/asm/cmpxchg_64.h index faa2f61..000f7d7 100644 --- a/arch/sparc/include/asm/cmpxchg_64.h +++ b/arch/sparc/include/asm/cmpxchg_64.h @@ -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: -- cgit v1.1