From c867b5ab1ff00fae7f5d89bc0c5f273c40f37f90 Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Wed, 16 Mar 2016 21:18:33 +0000 Subject: [bitops] Add generic atomic bit test, set, and clear functions Signed-off-by: Michael Brown --- src/arch/x86/include/bits/bitops.h | 94 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 94 insertions(+) create mode 100644 src/arch/x86/include/bits/bitops.h (limited to 'src/arch') diff --git a/src/arch/x86/include/bits/bitops.h b/src/arch/x86/include/bits/bitops.h new file mode 100644 index 000000000..17dcf1024 --- /dev/null +++ b/src/arch/x86/include/bits/bitops.h @@ -0,0 +1,94 @@ +#ifndef _BITS_BITOPS_H +#define _BITS_BITOPS_H + +/** @file + * + * x86 bit operations + * + * We perform atomic bit set and bit clear operations using "lock bts" + * and "lock btr". We use the output constraint to inform the + * compiler that any memory from the start of the bit field up to and + * including the byte containing the bit may be modified. (This is + * overkill but shouldn't matter in practice since we're unlikely to + * subsequently read other bits from the same bit field.) + */ + +FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ); + +#include + +/** + * Set bit atomically + * + * @v bit Bit to set + * @v bits Bit field + */ +static inline __attribute__ (( always_inline )) void +set_bit ( unsigned int bit, volatile void *bits ) { + volatile struct { + uint8_t byte[ ( bit / 8 ) + 1 ]; + } *bytes = bits; + + __asm__ __volatile__ ( "lock bts %1, %0" + : "+m" ( *bytes ) : "Ir" ( bit ) ); +} + +/** + * Clear bit atomically + * + * @v bit Bit to set + * @v bits Bit field + */ +static inline __attribute__ (( always_inline )) void +clear_bit ( unsigned int bit, volatile void *bits ) { + volatile struct { + uint8_t byte[ ( bit / 8 ) + 1 ]; + } *bytes = bits; + + __asm__ __volatile__ ( "lock btr %1, %0" + : "+m" ( *bytes ) : "Ir" ( bit ) ); +} + +/** + * Test and set bit atomically + * + * @v bit Bit to set + * @v bits Bit field + * @ret old Old value of bit (zero or non-zero) + */ +static inline __attribute__ (( always_inline )) int +test_and_set_bit ( unsigned int bit, volatile void *bits ) { + volatile struct { + uint8_t byte[ ( bit / 8 ) + 1 ]; + } *bytes = bits; + int old; + + __asm__ __volatile__ ( "lock bts %2, %0\n\t" + "sbb %1, %1\n\t" + : "+m" ( *bytes ), "=r" ( old ) + : "Ir" ( bit ) ); + return old; +} + +/** + * Test and clear bit atomically + * + * @v bit Bit to set + * @v bits Bit field + * @ret old Old value of bit (zero or non-zero) + */ +static inline __attribute__ (( always_inline )) int +test_and_clear_bit ( unsigned int bit, volatile void *bits ) { + volatile struct { + uint8_t byte[ ( bit / 8 ) + 1 ]; + } *bytes = bits; + int old; + + __asm__ __volatile__ ( "lock btr %2, %0\n\t" + "sbb %1, %1\n\t" + : "+m" ( *bytes ), "=r" ( old ) + : "Ir" ( bit ) ); + return old; +} + +#endif /* _BITS_BITOPS_H */ -- cgit v1.2.3-55-g7522