xref: /openbmc/u-boot/common/memsize.c (revision 21cd5815)
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(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 }
95