Linux Kernel  3.7.1
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memory.c
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1 /* -*- linux-c -*- ------------------------------------------------------- *
2  *
3  * Copyright (C) 1991, 1992 Linus Torvalds
4  * Copyright 2007 rPath, Inc. - All Rights Reserved
5  * Copyright 2009 Intel Corporation; author H. Peter Anvin
6  *
7  * This file is part of the Linux kernel, and is made available under
8  * the terms of the GNU General Public License version 2.
9  *
10  * ----------------------------------------------------------------------- */
11 
12 /*
13  * Memory detection code
14  */
15 
16 #include "boot.h"
17 
18 #define SMAP 0x534d4150 /* ASCII "SMAP" */
19 
20 static int detect_memory_e820(void)
21 {
22  int count = 0;
23  struct biosregs ireg, oreg;
24  struct e820entry *desc = boot_params.e820_map;
25  static struct e820entry buf; /* static so it is zeroed */
26 
27  initregs(&ireg);
28  ireg.ax = 0xe820;
29  ireg.cx = sizeof buf;
30  ireg.edx = SMAP;
31  ireg.di = (size_t)&buf;
32 
33  /*
34  * Note: at least one BIOS is known which assumes that the
35  * buffer pointed to by one e820 call is the same one as
36  * the previous call, and only changes modified fields. Therefore,
37  * we use a temporary buffer and copy the results entry by entry.
38  *
39  * This routine deliberately does not try to account for
40  * ACPI 3+ extended attributes. This is because there are
41  * BIOSes in the field which report zero for the valid bit for
42  * all ranges, and we don't currently make any use of the
43  * other attribute bits. Revisit this if we see the extended
44  * attribute bits deployed in a meaningful way in the future.
45  */
46 
47  do {
48  intcall(0x15, &ireg, &oreg);
49  ireg.ebx = oreg.ebx; /* for next iteration... */
50 
51  /* BIOSes which terminate the chain with CF = 1 as opposed
52  to %ebx = 0 don't always report the SMAP signature on
53  the final, failing, probe. */
54  if (oreg.eflags & X86_EFLAGS_CF)
55  break;
56 
57  /* Some BIOSes stop returning SMAP in the middle of
58  the search loop. We don't know exactly how the BIOS
59  screwed up the map at that point, we might have a
60  partial map, the full map, or complete garbage, so
61  just return failure. */
62  if (oreg.eax != SMAP) {
63  count = 0;
64  break;
65  }
66 
67  *desc++ = buf;
68  count++;
69  } while (ireg.ebx && count < ARRAY_SIZE(boot_params.e820_map));
70 
71  return boot_params.e820_entries = count;
72 }
73 
74 static int detect_memory_e801(void)
75 {
76  struct biosregs ireg, oreg;
77 
78  initregs(&ireg);
79  ireg.ax = 0xe801;
80  intcall(0x15, &ireg, &oreg);
81 
82  if (oreg.eflags & X86_EFLAGS_CF)
83  return -1;
84 
85  /* Do we really need to do this? */
86  if (oreg.cx || oreg.dx) {
87  oreg.ax = oreg.cx;
88  oreg.bx = oreg.dx;
89  }
90 
91  if (oreg.ax > 15*1024) {
92  return -1; /* Bogus! */
93  } else if (oreg.ax == 15*1024) {
94  boot_params.alt_mem_k = (oreg.bx << 6) + oreg.ax;
95  } else {
96  /*
97  * This ignores memory above 16MB if we have a memory
98  * hole there. If someone actually finds a machine
99  * with a memory hole at 16MB and no support for
100  * 0E820h they should probably generate a fake e820
101  * map.
102  */
103  boot_params.alt_mem_k = oreg.ax;
104  }
105 
106  return 0;
107 }
108 
109 static int detect_memory_88(void)
110 {
111  struct biosregs ireg, oreg;
112 
113  initregs(&ireg);
114  ireg.ah = 0x88;
115  intcall(0x15, &ireg, &oreg);
116 
117  boot_params.screen_info.ext_mem_k = oreg.ax;
118 
119  return -(oreg.eflags & X86_EFLAGS_CF); /* 0 or -1 */
120 }
121 
122 int detect_memory(void)
123 {
124  int err = -1;
125 
126  if (detect_memory_e820() > 0)
127  err = 0;
128 
129  if (!detect_memory_e801())
130  err = 0;
131 
132  if (!detect_memory_88())
133  err = 0;
134 
135  return err;
136 }
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