arch/sh/lib64/copy_page.S

   1 /*
   2    Copyright 2003 Richard Curnow, SuperH (UK) Ltd.
   3
   4    This file is subject to the terms and conditions of the GNU General Public
   5    License.  See the file "COPYING" in the main directory of this archive
   6    for more details.
   7
   8    Tight version of mempy for the case of just copying a page.
   9    Prefetch strategy empirically optimised against RTL simulations
  10    of SH5-101 cut2 eval chip with Cayman board DDR memory.
  11
  12    Parameters:
  13    r2 : destination effective address (start of page)
  14    r3 : source effective address (start of page)
  15
  16    Always copies 4096 bytes.
  17
  18    Points to review.
  19    * Currently the prefetch is 4 lines ahead and the alloco is 2 lines ahead.
  20      It seems like the prefetch needs to be at at least 4 lines ahead to get
  21      the data into the cache in time, and the allocos contend with outstanding
  22      prefetches for the same cache set, so it's better to have the numbers
  23      different.
  24    */
  25
  26         .section .text..SHmedia32,"ax"
  27         .little
  28
  29         .balign 8
  30         .global copy_page
  31 copy_page:
  32
  33         /* Copy 4096 bytes worth of data from r3 to r2.
  34            Do prefetches 4 lines ahead.
  35            Do alloco 2 lines ahead */
  36
  37         pta 1f, tr1
  38         pta 2f, tr2
  39         pta 3f, tr3
  40         ptabs r18, tr0
  41
  42 #if 0
  43         /* TAKum03020 */
  44         ld.q r3, 0x00, r63
  45         ld.q r3, 0x20, r63
  46         ld.q r3, 0x40, r63
  47         ld.q r3, 0x60, r63
  48 #endif
  49         alloco r2, 0x00
  50         synco           ! TAKum03020
  51         alloco r2, 0x20
  52         synco           ! TAKum03020
  53
  54         movi 3968, r6
  55         add  r2, r6, r6
  56         addi r6, 64, r7
  57         addi r7, 64, r8
  58         sub r3, r2, r60
  59         addi r60, 8, r61
  60         addi r61, 8, r62
  61         addi r62, 8, r23
  62         addi r60, 0x80, r22
  63
  64 /* Minimal code size.  The extra branches inside the loop don't cost much
  65    because they overlap with the time spent waiting for prefetches to
  66    complete. */
  67 1:
  68 #if 0
  69         /* TAKum03020 */
  70         bge/u r2, r6, tr2  ! skip prefetch for last 4 lines
  71         ldx.q r2, r22, r63 ! prefetch 4 lines hence
  72 #endif
  73 2:
  74         bge/u r2, r7, tr3  ! skip alloco for last 2 lines
  75         alloco r2, 0x40    ! alloc destination line 2 lines ahead
  76         synco           ! TAKum03020
  77 3:
  78         ldx.q r2, r60, r36
  79         ldx.q r2, r61, r37
  80         ldx.q r2, r62, r38
  81         ldx.q r2, r23, r39
  82         st.q  r2,   0, r36
  83         st.q  r2,   8, r37
  84         st.q  r2,  16, r38
  85         st.q  r2,  24, r39
  86         addi r2, 32, r2
  87         bgt/l r8, r2, tr1
  88
  89         blink tr0, r63     ! return