common/memsize.c

   1 /*
   2  * (C) Copyright 2004
   3  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
   4  *
   5  * SPDX-License-Identifier:     GPL-2.0+
   6  */
   7
   8 #include <config.h>
   9 #ifdef __PPC__
  10 /*
  11  * At least on G2 PowerPC cores, sequential accesses to non-existent
  12  * memory must be synchronized.
  13  */
  14 # include <asm/io.h>    /* for sync() */
  15 #else
  16 # define sync()         /* nothing */
  17 #endif
  18
  19 /*
  20  * Check memory range for valid RAM. A simple memory test determines
  21  * the actually available RAM size between addresses `base' and
  22  * `base + maxsize'.
  23  */
  24 long get_ram_size(long *base, long maxsize)
  25 {
  26         volatile long *addr;
  27         long           save[32];
  28         long           cnt;
  29         long           val;
  30         long           size;
  31         int            i = 0;
  32
  33         for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {
  34                 addr = base + cnt;      /* pointer arith! */
  35                 sync ();
  36                 save[i++] = *addr;
  37                 sync ();
  38                 *addr = ~cnt;
  39         }
  40
  41         addr = base;
  42         sync ();
  43         save[i] = *addr;
  44         sync ();
  45         *addr = 0;
  46
  47         sync ();
  48         if ((val = *addr) != 0) {
  49                 /* Restore the original data before leaving the function.
  50                  */
  51                 sync ();
  52                 *addr = save[i];
  53                 for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
  54                         addr  = base + cnt;
  55                         sync ();
  56                         *addr = save[--i];
  57                 }
  58                 return (0);
  59         }
  60
  61         for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
  62                 addr = base + cnt;      /* pointer arith! */
  63                 val = *addr;
  64                 *addr = save[--i];
  65                 if (val != ~cnt) {
  66                         size = cnt * sizeof (long);
  67                         /* Restore the original data before leaving the function.
  68                          */
  69                         for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
  70                                 addr  = base + cnt;
  71                                 *addr = save[--i];
  72                         }
  73                         return (size);
  74                 }
  75         }
  76
  77         return (maxsize);
  78 }