arch/m68k/mm/hwtest.c

   1 /* Tests for presence or absence of hardware registers.
   2  * This code was originally in atari/config.c, but I noticed
   3  * that it was also in drivers/nubus/nubus.c and I wanted to
   4  * use it in hp300/config.c, so it seemed sensible to pull it
   5  * out into its own file.
   6  *
   7  * The test is for use when trying to read a hardware register
   8  * that isn't present would cause a bus error. We set up a
   9  * temporary handler so that this doesn't kill the kernel.
  10  *
  11  * There is a test-by-reading and a test-by-writing; I present
  12  * them here complete with the comments from the original atari
  13  * config.c...
  14  *                -- PMM <pmaydell@chiark.greenend.org.uk>, 05/1998
  15  */
  16
  17 /* This function tests for the presence of an address, specially a
  18  * hardware register address. It is called very early in the kernel
  19  * initialization process, when the VBR register isn't set up yet. On
  20  * an Atari, it still points to address 0, which is unmapped. So a bus
  21  * error would cause another bus error while fetching the exception
  22  * vector, and the CPU would do nothing at all. So we needed to set up
  23  * a temporary VBR and a vector table for the duration of the test.
  24  */
  25
  26 #include <linux/module.h>
  27
  28 int hwreg_present( volatile void *regp )
  29 {
  30     int ret = 0;
  31     long        save_sp, save_vbr;
  32     long        tmp_vectors[3];
  33
  34     __asm__ __volatile__
  35         (       "movec  %/vbr,%2\n\t"
  36                 "movel  #Lberr1,%4@(8)\n\t"
  37                 "movec  %4,%/vbr\n\t"
  38                 "movel  %/sp,%1\n\t"
  39                 "moveq  #0,%0\n\t"
  40                 "tstb   %3@\n\t"
  41                 "nop\n\t"
  42                 "moveq  #1,%0\n"
  43                 "Lberr1:\n\t"
  44                 "movel  %1,%/sp\n\t"
  45                 "movec  %2,%/vbr"
  46                 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
  47                 : "a" (regp), "a" (tmp_vectors)
  48                 );
  49
  50     return( ret );
  51 }
  52 EXPORT_SYMBOL(hwreg_present);
  53
  54 /* Basically the same, but writes a value into a word register, protected
  55  * by a bus error handler. Returns 1 if successful, 0 otherwise.
  56  */
  57
  58 int hwreg_write( volatile void *regp, unsigned short val )
  59 {
  60         int             ret;
  61         long    save_sp, save_vbr;
  62         long    tmp_vectors[3];
  63
  64         __asm__ __volatile__
  65         (       "movec  %/vbr,%2\n\t"
  66                 "movel  #Lberr2,%4@(8)\n\t"
  67                 "movec  %4,%/vbr\n\t"
  68                 "movel  %/sp,%1\n\t"
  69                 "moveq  #0,%0\n\t"
  70                 "movew  %5,%3@\n\t"
  71                 "nop    \n\t"   /* If this nop isn't present, 'ret' may already be
  72                                  * loaded with 1 at the time the bus error
  73                                  * happens! */
  74                 "moveq  #1,%0\n"
  75         "Lberr2:\n\t"
  76                 "movel  %1,%/sp\n\t"
  77                 "movec  %2,%/vbr"
  78                 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
  79                 : "a" (regp), "a" (tmp_vectors), "g" (val)
  80         );
  81
  82         return( ret );
  83 }
  84 EXPORT_SYMBOL(hwreg_write);
  85