/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Copyright 2023 Red Hat
 */

#ifndef UDS_CPU_H
#define UDS_CPU_H

#include <linux/cache.h>

/**
 * uds_prefetch_address() - Minimize cache-miss latency by attempting to move data into a CPU cache
 *                          before it is accessed.
 *
 * @address: the address to fetch (may be invalid)
 * @for_write: must be constant at compile time--false if for reading, true if for writing
 */
static inline void uds_prefetch_address(const void *address, bool for_write)
{
        /*
         * for_write won't be a constant if we are compiled with optimization turned off, in which
         * case prefetching really doesn't matter. clang can't figure out that if for_write is a
         * constant, it can be passed as the second, mandatorily constant argument to prefetch(),
         * at least currently on llvm 12.
         */
        if (__builtin_constant_p(for_write)) {
                if (for_write)
                        __builtin_prefetch(address, true);
                else
                        __builtin_prefetch(address, false);
        }
}

/**
 * uds_prefetch_range() - Minimize cache-miss latency by attempting to move a range of addresses
 *                        into a CPU cache before they are accessed.
 *
 * @start: the starting address to fetch (may be invalid)
 * @size: the number of bytes in the address range
 * @for_write: must be constant at compile time--false if for reading, true if for writing
 */
static inline void uds_prefetch_range(const void *start, unsigned int size,
                                      bool for_write)
{
        /*
         * Count the number of cache lines to fetch, allowing for the address range to span an
         * extra cache line boundary due to address alignment.
         */
        const char *address = (const char *) start;
        unsigned int offset = ((uintptr_t) address % L1_CACHE_BYTES);
        unsigned int cache_lines = (1 + ((size + offset) / L1_CACHE_BYTES));

        while (cache_lines-- > 0) {
                uds_prefetch_address(address, for_write);
                address += L1_CACHE_BYTES;
        }
}

#endif /* UDS_CPU_H */