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         unsigned long flags;
  32         long save_sp, save_vbr;
  33         long tmp_vectors[3];
  34
  35         local_irq_save(flags);
  36         __asm__ __volatile__ (
  37                 "movec %/vbr,%2\n\t"
  38                 "movel #Lberr1,%4@(8)\n\t"
  39                 "movec %4,%/vbr\n\t"
  40                 "movel %/sp,%1\n\t"
  41                 "moveq #0,%0\n\t"
  42                 "tstb %3@\n\t"
  43                 "nop\n\t"
  44                 "moveq #1,%0\n"
  45         "Lberr1:\n\t"
  46                 "movel %1,%/sp\n\t"
  47                 "movec %2,%/vbr"
  48                 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
  49                 : "a" (regp), "a" (tmp_vectors)
  50         );
  51         local_irq_restore(flags);
  52
  53         return ret;
  54 }
  55 EXPORT_SYMBOL(hwreg_present);
  56
  57 /* Basically the same, but writes a value into a word register, protected
  58  * by a bus error handler. Returns 1 if successful, 0 otherwise.
  59  */
  60
  61 int hwreg_write(volatile void *regp, unsigned short val)
  62 {
  63         int ret;
  64         unsigned long flags;
  65         long save_sp, save_vbr;
  66         long tmp_vectors[3];
  67
  68         local_irq_save(flags);
  69         __asm__ __volatile__ (
  70                 "movec %/vbr,%2\n\t"
  71                 "movel #Lberr2,%4@(8)\n\t"
  72                 "movec %4,%/vbr\n\t"
  73                 "movel %/sp,%1\n\t"
  74                 "moveq #0,%0\n\t"
  75                 "movew %5,%3@\n\t"
  76                 "nop\n\t"
  77                 /*
  78                  * If this nop isn't present, 'ret' may already be loaded
  79                  * with 1 at the time the bus error happens!
  80                  */
  81                 "moveq #1,%0\n"
  82         "Lberr2:\n\t"
  83                 "movel %1,%/sp\n\t"
  84                 "movec %2,%/vbr"
  85                 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
  86                 : "a" (regp), "a" (tmp_vectors), "g" (val)
  87         );
  88         local_irq_restore(flags);
  89
  90         return ret;
  91 }
  92 EXPORT_SYMBOL(hwreg_write);
  93