atomic_xtensa.h

Go to the documentation of this file.

/*
 * Copyright (c) 2021, 2026 Intel Corporation
 * SPDX-License-Identifier: Apache-2.0
 */
 
#ifndef ZEPHYR_INCLUDE_ATOMIC_XTENSA_H_
#define ZEPHYR_INCLUDE_ATOMIC_XTENSA_H_
 
/* Included from <zephyr/sys/atomic.h> */
 
#include <xtensa/config/core-isa.h>
 
/* Recent GCC versions actually do have working atomics support on
 * Xtensa with S32C1I and so should work with CONFIG_ATOMIC_OPERATIONS_BUILTIN.
 * Existing versions of Xtensa's XCC do not and GCC also do not support
 * L32EX/S32EX.  So we define an inline implementation here for atomic CAS.
 */

static ALWAYS_INLINE atomic_val_t atomic_get(const atomic_t *target)
{
        atomic_val_t ret;
 
        /* Actual Xtensa hardware seems to have only in-order
         * pipelines, but the architecture does define a barrier load,
         * so use it.  There is a matching s32ri instruction, but
         * nothing in the Zephyr API requires a barrier store (all the
         * atomic write ops have exchange semantics.
         */
        __asm__ volatile("l32ai %0, %1, 0"
                         : "=r"(ret) : "r"(target) : "memory");
        return ret;
}

 
#if XCHAL_HAVE_EXCLUSIVE || defined(__DOXYGEN__)
 
/*
 * This utilizes L32EX/S32EX instructions to perform compare-and-set atomic
 * operation. This will unconditionally read from the atomic variable at @p addr
 * before the comparison. This value is returned from the function.
 */
static ALWAYS_INLINE
atomic_val_t xtensa_cas(atomic_t *addr, atomic_val_t oldval,
                        atomic_val_t newval)
{
        atomic_val_t mem_val;
        uint32_t v = newval;
 
        /* Read from address and mark it for exclusive access. */
        __asm__ volatile("l32ex %0, %1" : "=r"(mem_val) : "r"(addr));
 
        if (mem_val == oldval) {
                uint32_t result;
 
                __asm__ volatile("s32ex %1, %2; getex %0" : "=r"(result), "+r"(v) : "r"(addr));
 
                /* If GETEX returns store successful, we return the old value.
                 * Otherwise, we must return some other value to signal that
                 * the store failed to function caller.
                 */
                return (result == 1U) ? oldval : newval;
        }
 
        /* Since *addr != oldval, we skip writing to memory and
         * need to remove the exclusive lock before returning.
         */
        __asm__("clrex");
 
        return newval;
}
 
#elif XCHAL_HAVE_S32C1I
 
/*
 * This utilizes SCOMPARE1 register and s32c1i instruction to
 * perform compare-and-set atomic operation. This will
 * unconditionally read from the atomic variable at @p addr
 * before the comparison. This value is returned from
 * the function.
 */
static ALWAYS_INLINE
atomic_val_t xtensa_cas(atomic_t *addr, atomic_val_t oldval,
                        atomic_val_t newval)
{
        __asm__ volatile("wsr %1, SCOMPARE1; s32c1i %0, %2, 0"
                         : "+r"(newval), "+r"(oldval) : "r"(addr) : "memory");
 
        return newval; /* got swapped with the old memory by s32c1i */
}
 
#else
#error "No available hardware support for atomic operations"
#endif

static ALWAYS_INLINE
bool atomic_cas(atomic_t *target, atomic_val_t oldval, atomic_val_t newval)
{
        return oldval == xtensa_cas(target, oldval, newval);
}

static ALWAYS_INLINE
bool atomic_ptr_cas(atomic_ptr_t *target, void *oldval, void *newval)
{
        return (atomic_val_t) oldval
                == xtensa_cas((atomic_t *) target, (atomic_val_t) oldval,
                              (atomic_val_t) newval);
}
 
/* Generates an atomic exchange sequence that swaps the value at
 * address "target", whose old value is read to be "cur", with the
 * specified expression.  Evaluates to the old value which was
 * atomically replaced.
 */
#define Z__GEN_ATOMXCHG(expr) ({                                \
        atomic_val_t res, cur;                          \
        do {                                            \
                cur = *target;                          \
                res = xtensa_cas(target, cur, (expr));  \
        } while (res != cur);                           \
        res; })

static ALWAYS_INLINE
atomic_val_t atomic_set(atomic_t *target, atomic_val_t value)
{
        return Z__GEN_ATOMXCHG(value);
}

static ALWAYS_INLINE
atomic_val_t atomic_add(atomic_t *target, atomic_val_t value)
{
        return Z__GEN_ATOMXCHG(cur + value);
}

static ALWAYS_INLINE
atomic_val_t atomic_sub(atomic_t *target, atomic_val_t value)
{
        return Z__GEN_ATOMXCHG(cur - value);
}

static ALWAYS_INLINE
atomic_val_t atomic_inc(atomic_t *target)
{
        return Z__GEN_ATOMXCHG(cur + 1);
}

static ALWAYS_INLINE
atomic_val_t atomic_dec(atomic_t *target)
{
        return Z__GEN_ATOMXCHG(cur - 1);
}

static ALWAYS_INLINE atomic_val_t atomic_or(atomic_t *target,
                                            atomic_val_t value)
{
        return Z__GEN_ATOMXCHG(cur | value);
}

static ALWAYS_INLINE atomic_val_t atomic_xor(atomic_t *target,
                                             atomic_val_t value)
{
        return Z__GEN_ATOMXCHG(cur ^ value);
}

static ALWAYS_INLINE atomic_val_t atomic_and(atomic_t *target,
                                             atomic_val_t value)
{
        return Z__GEN_ATOMXCHG(cur & value);
}

static ALWAYS_INLINE atomic_val_t atomic_nand(atomic_t *target,
                                              atomic_val_t value)
{
        return Z__GEN_ATOMXCHG(~(cur & value));
}

static ALWAYS_INLINE void *atomic_ptr_get(const atomic_ptr_t *target)
{
        return (void *) atomic_get((atomic_t *)target);
}

static ALWAYS_INLINE void *atomic_ptr_set(atomic_ptr_t *target, void *value)
{
        return (void *) atomic_set((atomic_t *) target, (atomic_val_t) value);
}

static ALWAYS_INLINE atomic_val_t atomic_clear(atomic_t *target)
{
        return atomic_set(target, 0);
}

static ALWAYS_INLINE void *atomic_ptr_clear(atomic_ptr_t *target)
{
        return (void *) atomic_set((atomic_t *) target, 0);
}
 
#endif /* ZEPHYR_INCLUDE_ATOMIC_XTENSA_H_ */