/*
 * Copyright 2011 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 */

#include <linux/types.h>
#include <linux/string.h>
#include <linux/module.h>
/* EXPORT_SYMBOL() is in arch/tile/lib/exports.c since this should be asm. */

/* Must be 8 bytes in size. */
#define word_t uint64_t

#if CHIP_L2_LINE_SIZE() != 64 && CHIP_L2_LINE_SIZE() != 128
#error "Assumes 64 or 128 byte line size"
#endif

/* How many cache lines ahead should we prefetch? */
#define PREFETCH_LINES_AHEAD 3

/*
 * Provide "base versions" of load and store for the normal code path.
 * The kernel provides other versions for userspace copies.
 */
#define ST(p, v) (*(p) = (v))
#define LD(p) (*(p))

#ifndef USERCOPY_FUNC
#define ST1 ST
#define ST2 ST
#define ST4 ST
#define ST8 ST
#define LD1 LD
#define LD2 LD
#define LD4 LD
#define LD8 LD
#define RETVAL dstv
void *memcpy(void *__restrict dstv, const void *__restrict srcv, size_t n)
#else
/*
 * Special kernel version will provide implementation of the LDn/STn
 * macros to return a count of uncopied bytes due to mm fault.
 */
#define RETVAL 0
int USERCOPY_FUNC(void *__restrict dstv, const void *__restrict srcv, size_t n)
#endif
{
        char *__restrict dst1 = (char *)dstv;
        const char *__restrict src1 = (const char *)srcv;
        const char *__restrict src1_end;
        const char *__restrict prefetch;
        word_t *__restrict dst8;    /* 8-byte pointer to destination memory. */
        word_t final; /* Final bytes to write to trailing word, if any */
        long i;

        if (n < 16) {
                for (; n; n--)
                        ST1(dst1++, LD1(src1++));
                return RETVAL;
        }

        /*
         * Locate the end of source memory we will copy.  Don't
         * prefetch past this.
         */
        src1_end = src1 + n - 1;

        /* Prefetch ahead a few cache lines, but not past the end. */
        prefetch = src1;
        for (i = 0; i < PREFETCH_LINES_AHEAD; i++) {
                __insn_prefetch(prefetch);
                prefetch += CHIP_L2_LINE_SIZE();
                prefetch = (prefetch > src1_end) ? prefetch : src1;
        }

        /* Copy bytes until dst is word-aligned. */
        for (; (uintptr_t)dst1 & (sizeof(word_t) - 1); n--)
                ST1(dst1++, LD1(src1++));

        /* 8-byte pointer to destination memory. */
        dst8 = (word_t *)dst1;

        if (__builtin_expect((uintptr_t)src1 & (sizeof(word_t) - 1), 0)) {
                /*
                 * Misaligned copy.  Copy 8 bytes at a time, but don't
                 * bother with other fanciness.
                 *
                 * TODO: Consider prefetching and using wh64 as well.
                 */

                /* Create an aligned src8. */
                const word_t *__restrict src8 =
                        (const word_t *)((uintptr_t)src1 & -sizeof(word_t));
                word_t b;

                word_t a = LD8(src8++);
                for (; n >= sizeof(word_t); n -= sizeof(word_t)) {
                        b = LD8(src8++);
                        a = __insn_dblalign(a, b, src1);
                        ST8(dst8++, a);
                        a = b;
                }

                if (n == 0)
                        return RETVAL;

                b = ((const char *)src8 <= src1_end) ? *src8 : 0;

                /*
                 * Final source bytes to write to trailing partial
                 * word, if any.
                 */
                final = __insn_dblalign(a, b, src1);
        } else {
                /* Aligned copy. */

                const word_t* __restrict src8 = (const word_t *)src1;

                /* src8 and dst8 are both word-aligned. */
                if (n >= CHIP_L2_LINE_SIZE()) {
                        /* Copy until 'dst' is cache-line-aligned. */
                        for (; (uintptr_t)dst8 & (CHIP_L2_LINE_SIZE() - 1);
                             n -= sizeof(word_t))
                                ST8(dst8++, LD8(src8++));

                        for (; n >= CHIP_L2_LINE_SIZE(); ) {
                                __insn_wh64(dst8);

                                /*
                                 * Prefetch and advance to next line
                                 * to prefetch, but don't go past the end
                                 */
                                __insn_prefetch(prefetch);
                                prefetch += CHIP_L2_LINE_SIZE();
                                prefetch = (prefetch > src1_end) ? prefetch :
                                        (const char *)src8;

                                /*
                                 * Copy an entire cache line.  Manually
                                 * unrolled to avoid idiosyncracies of
                                 * compiler unrolling.
                                 */
#define COPY_WORD(offset) ({ ST8(dst8+offset, LD8(src8+offset)); n -= 8; })
                                COPY_WORD(0);
                                COPY_WORD(1);
                                COPY_WORD(2);
                                COPY_WORD(3);
                                COPY_WORD(4);
                                COPY_WORD(5);
                                COPY_WORD(6);
                                COPY_WORD(7);
#if CHIP_L2_LINE_SIZE() == 128
                                COPY_WORD(8);
                                COPY_WORD(9);
                                COPY_WORD(10);
                                COPY_WORD(11);
                                COPY_WORD(12);
                                COPY_WORD(13);
                                COPY_WORD(14);
                                COPY_WORD(15);
#elif CHIP_L2_LINE_SIZE() != 64
# error Fix code that assumes particular L2 cache line sizes
#endif

                                dst8 += CHIP_L2_LINE_SIZE() / sizeof(word_t);
                                src8 += CHIP_L2_LINE_SIZE() / sizeof(word_t);
                        }
                }

                for (; n >= sizeof(word_t); n -= sizeof(word_t))
                        ST8(dst8++, LD8(src8++));

                if (__builtin_expect(n == 0, 1))
                        return RETVAL;

                final = LD8(src8);
        }

        /* n != 0 if we get here.  Write out any trailing bytes. */
        dst1 = (char *)dst8;
#ifndef __BIG_ENDIAN__
        if (n & 4) {
                ST4((uint32_t *)dst1, final);
                dst1 += 4;
                final >>= 32;
                n &= 3;
        }
        if (n & 2) {
                ST2((uint16_t *)dst1, final);
                dst1 += 2;
                final >>= 16;
                n &= 1;
        }
        if (n)
                ST1((uint8_t *)dst1, final);
#else
        if (n & 4) {
                ST4((uint32_t *)dst1, final >> 32);
                dst1 += 4;
        }
        else
        {
                final >>= 32;
        }
        if (n & 2) {
                ST2((uint16_t *)dst1, final >> 16);
                dst1 += 2;
        }
        else
        {
                final >>= 16;
        }
        if (n & 1)
                ST1((uint8_t *)dst1, final >> 8);
#endif

        return RETVAL;
}

#ifdef USERCOPY_FUNC
#undef ST1
#undef ST2
#undef ST4
#undef ST8
#undef LD1
#undef LD2
#undef LD4
#undef LD8
#undef USERCOPY_FUNC
#endif