/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Unified implementation of memcpy, memmove and the __copy_user backend.
 *
 * Copyright (C) 1998, 99, 2000, 01, 2002 Ralf Baechle (ralf@gnu.org)
 * Copyright (C) 1999, 2000, 01, 2002 Silicon Graphics, Inc.
 * Copyright (C) 2002 Broadcom, Inc.
 *   memcpy/copy_user author: Mark Vandevoorde
 * Copyright (C) 2007  Maciej W. Rozycki
 *
 * Mnemonic names for arguments to memcpy/__copy_user
 */

/*
 * Hack to resolve longstanding prefetch issue
 *
 * Prefetching may be fatal on some systems if we're prefetching beyond the
 * end of memory on some systems.  It's also a seriously bad idea on non
 * dma-coherent systems.
 */
#ifdef CONFIG_DMA_NONCOHERENT
#undef CONFIG_CPU_HAS_PREFETCH
#endif
#ifdef CONFIG_MIPS_MALTA
#undef CONFIG_CPU_HAS_PREFETCH
#endif

#include <asm/asm.h>
#include <asm/asm-offsets.h>
#include <asm/regdef.h>

#define dst a0
#define src a1
#define len a2

/*
 * Spec
 *
 * memcpy copies len bytes from src to dst and sets v0 to dst.
 * It assumes that
 *   - src and dst don't overlap
 *   - src is readable
 *   - dst is writable
 * memcpy uses the standard calling convention
 *
 * __copy_user copies up to len bytes from src to dst and sets a2 (len) to
 * the number of uncopied bytes due to an exception caused by a read or write.
 * __copy_user assumes that src and dst don't overlap, and that the call is
 * implementing one of the following:
 *   copy_to_user
 *     - src is readable  (no exceptions when reading src)
 *   copy_from_user
 *     - dst is writable  (no exceptions when writing dst)
 * __copy_user uses a non-standard calling convention; see
 * include/asm-mips/uaccess.h
 *
 * When an exception happens on a load, the handler must
 # ensure that all of the destination buffer is overwritten to prevent
 * leaking information to user mode programs.
 */

/*
 * Implementation
 */

/*
 * The exception handler for loads requires that:
 *  1- AT contain the address of the byte just past the end of the source
 *     of the copy,
 *  2- src_entry <= src < AT, and
 *  3- (dst - src) == (dst_entry - src_entry),
 * The _entry suffix denotes values when __copy_user was called.
 *
 * (1) is set up up by uaccess.h and maintained by not writing AT in copy_user
 * (2) is met by incrementing src by the number of bytes copied
 * (3) is met by not doing loads between a pair of increments of dst and src
 *
 * The exception handlers for stores adjust len (if necessary) and return.
 * These handlers do not need to overwrite any data.
 *
 * For __rmemcpy and memmove an exception is always a kernel bug, therefore
 * they're not protected.
 */

#define EXC(inst_reg,addr,handler)              \
9:      inst_reg, addr;                         \
        .section __ex_table,"a";                \
        PTR     9b, handler;                    \
        .previous

/*
 * Only on the 64-bit kernel we can made use of 64-bit registers.
 */
#ifdef CONFIG_64BIT
#define USE_DOUBLE
#endif

#ifdef USE_DOUBLE

#define LOAD   ld
#define LOADL  ldl
#define LOADR  ldr
#define STOREL sdl
#define STORER sdr
#define STORE  sd
#define ADD    daddu
#define SUB    dsubu
#define SRL    dsrl
#define SRA    dsra
#define SLL    dsll
#define SLLV   dsllv
#define SRLV   dsrlv
#define NBYTES 8
#define LOG_NBYTES 3

/*
 * As we are sharing code base with the mips32 tree (which use the o32 ABI
 * register definitions). We need to redefine the register definitions from
 * the n64 ABI register naming to the o32 ABI register naming.
 */
#undef t0
#undef t1
#undef t2
#undef t3
#define t0      $8
#define t1      $9
#define t2      $10
#define t3      $11
#define t4      $12
#define t5      $13
#define t6      $14
#define t7      $15

#else

#define LOAD   lw
#define LOADL  lwl
#define LOADR  lwr
#define STOREL swl
#define STORER swr
#define STORE  sw
#define ADD    addu
#define SUB    subu
#define SRL    srl
#define SLL    sll
#define SRA    sra
#define SLLV   sllv
#define SRLV   srlv
#define NBYTES 4
#define LOG_NBYTES 2

#endif /* USE_DOUBLE */

#ifdef CONFIG_CPU_LITTLE_ENDIAN
#define LDFIRST LOADR
#define LDREST  LOADL
#define STFIRST STORER
#define STREST  STOREL
#define SHIFT_DISCARD SLLV
#else
#define LDFIRST LOADL
#define LDREST  LOADR
#define STFIRST STOREL
#define STREST  STORER
#define SHIFT_DISCARD SRLV
#endif

#define FIRST(unit) ((unit)*NBYTES)
#define REST(unit)  (FIRST(unit)+NBYTES-1)
#define UNIT(unit)  FIRST(unit)

#define ADDRMASK (NBYTES-1)

        .text
        .set    noreorder
#ifndef CONFIG_CPU_DADDI_WORKAROUNDS
        .set    noat
#else
        .set    at=v1
#endif

/*
 * A combined memcpy/__copy_user
 * __copy_user sets len to 0 for success; else to an upper bound of
 * the number of uncopied bytes.
 * memcpy sets v0 to dst.
 */
        .align  5
LEAF(__copy_user_inatomic)
        /*
         * Note: dst & src may be unaligned, len may be 0
         * Temps
         */
#define rem t8

        /*
         * The "issue break"s below are very approximate.
         * Issue delays for dcache fills will perturb the schedule, as will
         * load queue full replay traps, etc.
         *
         * If len < NBYTES use byte operations.
         */
        PREF(   0, 0(src) )
        PREF(   1, 0(dst) )
        sltu    t2, len, NBYTES
        and     t1, dst, ADDRMASK
        PREF(   0, 1*32(src) )
        PREF(   1, 1*32(dst) )
        bnez    t2, .Lcopy_bytes_checklen
         and    t0, src, ADDRMASK
        PREF(   0, 2*32(src) )
        PREF(   1, 2*32(dst) )
        bnez    t1, .Ldst_unaligned
         nop
        bnez    t0, .Lsrc_unaligned_dst_aligned
        /*
         * use delay slot for fall-through
         * src and dst are aligned; need to compute rem
         */
.Lboth_aligned:
         SRL    t0, len, LOG_NBYTES+3           # +3 for 8 units/iter
        beqz    t0, .Lcleanup_both_aligned      # len < 8*NBYTES
         and    rem, len, (8*NBYTES-1)          # rem = len % (8*NBYTES)
        PREF(   0, 3*32(src) )
        PREF(   1, 3*32(dst) )
        .align  4
1:
EXC(    LOAD    t0, UNIT(0)(src),       .Ll_exc)
EXC(    LOAD    t1, UNIT(1)(src),       .Ll_exc_copy)
EXC(    LOAD    t2, UNIT(2)(src),       .Ll_exc_copy)
EXC(    LOAD    t3, UNIT(3)(src),       .Ll_exc_copy)
        SUB     len, len, 8*NBYTES
EXC(    LOAD    t4, UNIT(4)(src),       .Ll_exc_copy)
EXC(    LOAD    t7, UNIT(5)(src),       .Ll_exc_copy)
        STORE   t0, UNIT(0)(dst)
        STORE   t1, UNIT(1)(dst)
EXC(    LOAD    t0, UNIT(6)(src),       .Ll_exc_copy)
EXC(    LOAD    t1, UNIT(7)(src),       .Ll_exc_copy)
        ADD     src, src, 8*NBYTES
        ADD     dst, dst, 8*NBYTES
        STORE   t2, UNIT(-6)(dst)
        STORE   t3, UNIT(-5)(dst)
        STORE   t4, UNIT(-4)(dst)
        STORE   t7, UNIT(-3)(dst)
        STORE   t0, UNIT(-2)(dst)
        STORE   t1, UNIT(-1)(dst)
        PREF(   0, 8*32(src) )
        PREF(   1, 8*32(dst) )
        bne     len, rem, 1b
         nop

        /*
         * len == rem == the number of bytes left to copy < 8*NBYTES
         */
.Lcleanup_both_aligned:
        beqz    len, .Ldone
         sltu   t0, len, 4*NBYTES
        bnez    t0, .Lless_than_4units
         and    rem, len, (NBYTES-1)    # rem = len % NBYTES
        /*
         * len >= 4*NBYTES
         */
EXC(    LOAD    t0, UNIT(0)(src),       .Ll_exc)
EXC(    LOAD    t1, UNIT(1)(src),       .Ll_exc_copy)
EXC(    LOAD    t2, UNIT(2)(src),       .Ll_exc_copy)
EXC(    LOAD    t3, UNIT(3)(src),       .Ll_exc_copy)
        SUB     len, len, 4*NBYTES
        ADD     src, src, 4*NBYTES
        STORE   t0, UNIT(0)(dst)
        STORE   t1, UNIT(1)(dst)
        STORE   t2, UNIT(2)(dst)
        STORE   t3, UNIT(3)(dst)
        .set    reorder                         /* DADDI_WAR */
        ADD     dst, dst, 4*NBYTES
        beqz    len, .Ldone
        .set    noreorder
.Lless_than_4units:
        /*
         * rem = len % NBYTES
         */
        beq     rem, len, .Lcopy_bytes
         nop
1:
EXC(    LOAD    t0, 0(src),             .Ll_exc)
        ADD     src, src, NBYTES
        SUB     len, len, NBYTES
        STORE   t0, 0(dst)
        .set    reorder                         /* DADDI_WAR */
        ADD     dst, dst, NBYTES
        bne     rem, len, 1b
        .set    noreorder

        /*
         * src and dst are aligned, need to copy rem bytes (rem < NBYTES)
         * A loop would do only a byte at a time with possible branch
         * mispredicts.  Can't do an explicit LOAD dst,mask,or,STORE
         * because can't assume read-access to dst.  Instead, use
         * STREST dst, which doesn't require read access to dst.
         *
         * This code should perform better than a simple loop on modern,
         * wide-issue mips processors because the code has fewer branches and
         * more instruction-level parallelism.
         */
#define bits t2
        beqz    len, .Ldone
         ADD    t1, dst, len    # t1 is just past last byte of dst
        li      bits, 8*NBYTES
        SLL     rem, len, 3     # rem = number of bits to keep
EXC(    LOAD    t0, 0(src),             .Ll_exc)
        SUB     bits, bits, rem # bits = number of bits to discard
        SHIFT_DISCARD t0, t0, bits
        STREST  t0, -1(t1)
        jr      ra
         move   len, zero
.Ldst_unaligned:
        /*
         * dst is unaligned
         * t0 = src & ADDRMASK
         * t1 = dst & ADDRMASK; T1 > 0
         * len >= NBYTES
         *
         * Copy enough bytes to align dst
         * Set match = (src and dst have same alignment)
         */
#define match rem
EXC(    LDFIRST t3, FIRST(0)(src),      .Ll_exc)
        ADD     t2, zero, NBYTES
EXC(    LDREST  t3, REST(0)(src),       .Ll_exc_copy)
        SUB     t2, t2, t1      # t2 = number of bytes copied
        xor     match, t0, t1
        STFIRST t3, FIRST(0)(dst)
        beq     len, t2, .Ldone
         SUB    len, len, t2
        ADD     dst, dst, t2
        beqz    match, .Lboth_aligned
         ADD    src, src, t2

.Lsrc_unaligned_dst_aligned:
        SRL     t0, len, LOG_NBYTES+2    # +2 for 4 units/iter
        PREF(   0, 3*32(src) )
        beqz    t0, .Lcleanup_src_unaligned
         and    rem, len, (4*NBYTES-1)   # rem = len % 4*NBYTES
        PREF(   1, 3*32(dst) )
1:
/*
 * Avoid consecutive LD*'s to the same register since some mips
 * implementations can't issue them in the same cycle.
 * It's OK to load FIRST(N+1) before REST(N) because the two addresses
 * are to the same unit (unless src is aligned, but it's not).
 */
EXC(    LDFIRST t0, FIRST(0)(src),      .Ll_exc)
EXC(    LDFIRST t1, FIRST(1)(src),      .Ll_exc_copy)
        SUB     len, len, 4*NBYTES
EXC(    LDREST  t0, REST(0)(src),       .Ll_exc_copy)
EXC(    LDREST  t1, REST(1)(src),       .Ll_exc_copy)
EXC(    LDFIRST t2, FIRST(2)(src),      .Ll_exc_copy)
EXC(    LDFIRST t3, FIRST(3)(src),      .Ll_exc_copy)
EXC(    LDREST  t2, REST(2)(src),       .Ll_exc_copy)
EXC(    LDREST  t3, REST(3)(src),       .Ll_exc_copy)
        PREF(   0, 9*32(src) )          # 0 is PREF_LOAD  (not streamed)
        ADD     src, src, 4*NBYTES
#ifdef CONFIG_CPU_SB1
        nop                             # improves slotting
#endif
        STORE   t0, UNIT(0)(dst)
        STORE   t1, UNIT(1)(dst)
        STORE   t2, UNIT(2)(dst)
        STORE   t3, UNIT(3)(dst)
        PREF(   1, 9*32(dst) )          # 1 is PREF_STORE (not streamed)
        .set    reorder                         /* DADDI_WAR */
        ADD     dst, dst, 4*NBYTES
        bne     len, rem, 1b
        .set    noreorder

.Lcleanup_src_unaligned:
        beqz    len, .Ldone
         and    rem, len, NBYTES-1  # rem = len % NBYTES
        beq     rem, len, .Lcopy_bytes
         nop
1:
EXC(    LDFIRST t0, FIRST(0)(src),      .Ll_exc)
EXC(    LDREST  t0, REST(0)(src),       .Ll_exc_copy)
        ADD     src, src, NBYTES
        SUB     len, len, NBYTES
        STORE   t0, 0(dst)
        .set    reorder                         /* DADDI_WAR */
        ADD     dst, dst, NBYTES
        bne     len, rem, 1b
        .set    noreorder

.Lcopy_bytes_checklen:
        beqz    len, .Ldone
         nop
.Lcopy_bytes:
        /* 0 < len < NBYTES  */
#define COPY_BYTE(N)                    \
EXC(    lb      t0, N(src), .Ll_exc);   \
        SUB     len, len, 1;            \
        beqz    len, .Ldone;            \
         sb     t0, N(dst)

        COPY_BYTE(0)
        COPY_BYTE(1)
#ifdef USE_DOUBLE
        COPY_BYTE(2)
        COPY_BYTE(3)
        COPY_BYTE(4)
        COPY_BYTE(5)
#endif
EXC(    lb      t0, NBYTES-2(src), .Ll_exc)
        SUB     len, len, 1
        jr      ra
         sb     t0, NBYTES-2(dst)
.Ldone:
        jr      ra
         nop
        END(__copy_user_inatomic)

.Ll_exc_copy:
        /*
         * Copy bytes from src until faulting load address (or until a
         * lb faults)
         *
         * When reached by a faulting LDFIRST/LDREST, THREAD_BUADDR($28)
         * may be more than a byte beyond the last address.
         * Hence, the lb below may get an exception.
         *
         * Assumes src < THREAD_BUADDR($28)
         */
        LOAD    t0, TI_TASK($28)
         nop
        LOAD    t0, THREAD_BUADDR(t0)
1:
EXC(    lb      t1, 0(src),     .Ll_exc)
        ADD     src, src, 1
        sb      t1, 0(dst)      # can't fault -- we're copy_from_user
        .set    reorder                         /* DADDI_WAR */
        ADD     dst, dst, 1
        bne     src, t0, 1b
        .set    noreorder
.Ll_exc:
        LOAD    t0, TI_TASK($28)
         nop
        LOAD    t0, THREAD_BUADDR(t0)   # t0 is just past last good address
         nop
        SUB     len, AT, t0             # len number of uncopied bytes
        jr      ra
         nop