1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Copyright (C) 2017 Imagination Technologies 4 * Author: Paul Burton <paul.burton@mips.com> 5 */ 6 7 #include <linux/bitops.h> 8 #include <asm/cmpxchg.h> 9 10 unsigned long __xchg_small(volatile void *ptr, unsigned long val, unsigned int size) 11 { 12 u32 old32, new32, load32, mask; 13 volatile u32 *ptr32; 14 unsigned int shift; 15 16 /* Check that ptr is naturally aligned */ 17 WARN_ON((unsigned long)ptr & (size - 1)); 18 19 /* Mask value to the correct size. */ 20 mask = GENMASK((size * BITS_PER_BYTE) - 1, 0); 21 val &= mask; 22 23 /* 24 * Calculate a shift & mask that correspond to the value we wish to 25 * exchange within the naturally aligned 4 byte integerthat includes 26 * it. 27 */ 28 shift = (unsigned long)ptr & 0x3; 29 if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN)) 30 shift ^= sizeof(u32) - size; 31 shift *= BITS_PER_BYTE; 32 mask <<= shift; 33 34 /* 35 * Calculate a pointer to the naturally aligned 4 byte integer that 36 * includes our byte of interest, and load its value. 37 */ 38 ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3); 39 load32 = *ptr32; 40 41 do { 42 old32 = load32; 43 new32 = (load32 & ~mask) | (val << shift); 44 load32 = arch_cmpxchg(ptr32, old32, new32); 45 } while (load32 != old32); 46 47 return (load32 & mask) >> shift; 48 } 49 50 unsigned long __cmpxchg_small(volatile void *ptr, unsigned long old, 51 unsigned long new, unsigned int size) 52 { 53 u32 mask, old32, new32, load32, load; 54 volatile u32 *ptr32; 55 unsigned int shift; 56 57 /* Check that ptr is naturally aligned */ 58 WARN_ON((unsigned long)ptr & (size - 1)); 59 60 /* Mask inputs to the correct size. */ 61 mask = GENMASK((size * BITS_PER_BYTE) - 1, 0); 62 old &= mask; 63 new &= mask; 64 65 /* 66 * Calculate a shift & mask that correspond to the value we wish to 67 * compare & exchange within the naturally aligned 4 byte integer 68 * that includes it. 69 */ 70 shift = (unsigned long)ptr & 0x3; 71 if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN)) 72 shift ^= sizeof(u32) - size; 73 shift *= BITS_PER_BYTE; 74 mask <<= shift; 75 76 /* 77 * Calculate a pointer to the naturally aligned 4 byte integer that 78 * includes our byte of interest, and load its value. 79 */ 80 ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3); 81 load32 = *ptr32; 82 83 while (true) { 84 /* 85 * Ensure the byte we want to exchange matches the expected 86 * old value, and if not then bail. 87 */ 88 load = (load32 & mask) >> shift; 89 if (load != old) 90 return load; 91 92 /* 93 * Calculate the old & new values of the naturally aligned 94 * 4 byte integer that include the byte we want to exchange. 95 * Attempt to exchange the old value for the new value, and 96 * return if we succeed. 97 */ 98 old32 = (load32 & ~mask) | (old << shift); 99 new32 = (load32 & ~mask) | (new << shift); 100 load32 = arch_cmpxchg(ptr32, old32, new32); 101 if (load32 == old32) 102 return old; 103 } 104 } 105