common/memsize.c

   1 /*
   2  * (C) Copyright 2004
   3  * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
   4  *
   5  * See file CREDITS for list of people who contributed to this
   6  * project.
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License as
  10  * published by the Free Software Foundation; either version 2 of
  11  * the License, or (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  21  * MA 02111-1307 USA
  22  */
  23
  24 #include <config.h>
  25 #ifdef __PPC__
  26 /*
  27  * At least on G2 PowerPC cores, sequential accesses to non-existent
  28  * memory must be synchronized.
  29  */
  30 # include <asm/io.h>    /* for sync() */
  31 #else
  32 # define sync()         /* nothing */
  33 #endif
  34
  35 /*
  36  * Check memory range for valid RAM. A simple memory test determines
  37  * the actually available RAM size between addresses `base' and
  38  * `base + maxsize'.
  39  */
  40 long get_ram_size(volatile long *base, long maxsize)
  41 {
  42         volatile long *addr;
  43         long           save[32];
  44         long           cnt;
  45         long           val;
  46         long           size;
  47         int            i = 0;
  48
  49         for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {
  50                 addr = base + cnt;      /* pointer arith! */
  51                 sync ();
  52                 save[i++] = *addr;
  53                 sync ();
  54                 *addr = ~cnt;
  55         }
  56
  57         addr = base;
  58         sync ();
  59         save[i] = *addr;
  60         sync ();
  61         *addr = 0;
  62
  63         sync ();
  64         if ((val = *addr) != 0) {
  65                 /* Restore the original data before leaving the function.
  66                  */
  67                 sync ();
  68                 *addr = save[i];
  69                 for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
  70                         addr  = base + cnt;
  71                         sync ();
  72                         *addr = save[--i];
  73                 }
  74                 return (0);
  75         }
  76
  77         for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
  78                 addr = base + cnt;      /* pointer arith! */
  79                 val = *addr;
  80                 *addr = save[--i];
  81                 if (val != ~cnt) {
  82                         size = cnt * sizeof (long);
  83                         /* Restore the original data before leaving the function.
  84                          */
  85                         for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
  86                                 addr  = base + cnt;
  87                                 *addr = save[--i];
  88                         }
  89                         return (size);
  90                 }
  91         }
  92
  93         return (maxsize);
  94 }