// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2017 Imagination Technologies
 * Author: Paul Burton <paul.burton@mips.com>
 */

#include <linux/bitops.h>
#include <asm/cmpxchg.h>

unsigned long __xchg_small(volatile void *ptr, unsigned long val, unsigned int size)
{
        u32 old32, new32, load32, mask;
        volatile u32 *ptr32;
        unsigned int shift;

        /* Check that ptr is naturally aligned */
        WARN_ON((unsigned long)ptr & (size - 1));

        /* Mask value to the correct size. */
        mask = GENMASK((size * BITS_PER_BYTE) - 1, 0);
        val &= mask;

        /*
         * Calculate a shift & mask that correspond to the value we wish to
         * exchange within the naturally aligned 4 byte integer that includes
         * it.
         */
        shift = (unsigned long)ptr & 0x3;
        if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
                shift ^= sizeof(u32) - size;
        shift *= BITS_PER_BYTE;
        mask <<= shift;

        /*
         * Calculate a pointer to the naturally aligned 4 byte integer that
         * includes our byte of interest, and load its value.
         */
        ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3);
        load32 = *ptr32;

        do {
                old32 = load32;
                new32 = (load32 & ~mask) | (val << shift);
                load32 = arch_cmpxchg(ptr32, old32, new32);
        } while (load32 != old32);

        return (load32 & mask) >> shift;
}

unsigned long __cmpxchg_small(volatile void *ptr, unsigned long old,
                              unsigned long new, unsigned int size)
{
        u32 mask, old32, new32, load32, load;
        volatile u32 *ptr32;
        unsigned int shift;

        /* Check that ptr is naturally aligned */
        WARN_ON((unsigned long)ptr & (size - 1));

        /* Mask inputs to the correct size. */
        mask = GENMASK((size * BITS_PER_BYTE) - 1, 0);
        old &= mask;
        new &= mask;

        /*
         * Calculate a shift & mask that correspond to the value we wish to
         * compare & exchange within the naturally aligned 4 byte integer
         * that includes it.
         */
        shift = (unsigned long)ptr & 0x3;
        if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
                shift ^= sizeof(u32) - size;
        shift *= BITS_PER_BYTE;
        mask <<= shift;

        /*
         * Calculate a pointer to the naturally aligned 4 byte integer that
         * includes our byte of interest, and load its value.
         */
        ptr32 = (volatile u32 *)((unsigned long)ptr & ~0x3);
        load32 = *ptr32;

        while (true) {
                /*
                 * Ensure the byte we want to exchange matches the expected
                 * old value, and if not then bail.
                 */
                load = (load32 & mask) >> shift;
                if (load != old)
                        return load;

                /*
                 * Calculate the old & new values of the naturally aligned
                 * 4 byte integer that include the byte we want to exchange.
                 * Attempt to exchange the old value for the new value, and
                 * return if we succeed.
                 */
                old32 = (load32 & ~mask) | (old << shift);
                new32 = (load32 & ~mask) | (new << shift);
                load32 = arch_cmpxchg(ptr32, old32, new32);
                if (load32 == old32)
                        return old;
        }
}
EXPORT_SYMBOL(__cmpxchg_small);