1 // SPDX-License-Identifier: GPL-2.0-only
2 /* -*- linux-c -*- ------------------------------------------------------- *
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 * Copyright 2007 rPath, Inc. - All Rights Reserved
6 * Copyright 2009 Intel Corporation; author H. Peter Anvin
7 *
8 * ----------------------------------------------------------------------- */
9
10 /*
11 * Memory detection code
12 */
13
14 #include "boot.h"
15
16 #define SMAP 0x534d4150 /* ASCII "SMAP" */
17
18 static void detect_memory_e820(void)
19 {
20 int count = 0;
21 struct biosregs ireg, oreg;
22 struct boot_e820_entry *desc = boot_params.e820_table;
23 static struct boot_e820_entry buf; /* static so it is zeroed */
24
25 initregs(&ireg);
26 ireg.ax = 0xe820;
27 ireg.cx = sizeof(buf);
28 ireg.edx = SMAP;
29 ireg.di = (size_t)&buf;
30
31 /*
32 * Note: at least one BIOS is known which assumes that the
33 * buffer pointed to by one e820 call is the same one as
34 * the previous call, and only changes modified fields. Therefore,
35 * we use a temporary buffer and copy the results entry by entry.
36 *
37 * This routine deliberately does not try to account for
38 * ACPI 3+ extended attributes. This is because there are
39 * BIOSes in the field which report zero for the valid bit for
40 * all ranges, and we don't currently make any use of the
41 * other attribute bits. Revisit this if we see the extended
42 * attribute bits deployed in a meaningful way in the future.
43 */
44
45 do {
46 intcall(0x15, &ireg, &oreg);
47 ireg.ebx = oreg.ebx; /* for next iteration... */
48
49 /* BIOSes which terminate the chain with CF = 1 as opposed
50 to %ebx = 0 don't always report the SMAP signature on
51 the final, failing, probe. */
52 if (oreg.eflags & X86_EFLAGS_CF)
53 break;
54
55 /* Some BIOSes stop returning SMAP in the middle of
56 the search loop. We don't know exactly how the BIOS
57 screwed up the map at that point, we might have a
58 partial map, the full map, or complete garbage, so
59 just return failure. */
60 if (oreg.eax != SMAP) {
61 count = 0;
62 break;
63 }
64
65 *desc++ = buf;
66 count++;
67 } while (ireg.ebx && count < ARRAY_SIZE(boot_params.e820_table));
68
69 boot_params.e820_entries = count;
70 }
71
72 static void detect_memory_e801(void)
73 {
74 struct biosregs ireg, oreg;
75
76 initregs(&ireg);
77 ireg.ax = 0xe801;
78 intcall(0x15, &ireg, &oreg);
79
80 if (oreg.eflags & X86_EFLAGS_CF)
81 return;
82
83 /* Do we really need to do this? */
84 if (oreg.cx || oreg.dx) {
85 oreg.ax = oreg.cx;
86 oreg.bx = oreg.dx;
87 }
88
89 if (oreg.ax > 15*1024) {
90 return; /* Bogus! */
91 } else if (oreg.ax == 15*1024) {
92 boot_params.alt_mem_k = (oreg.bx << 6) + oreg.ax;
93 } else {
94 /*
95 * This ignores memory above 16MB if we have a memory
96 * hole there. If someone actually finds a machine
97 * with a memory hole at 16MB and no support for
98 * 0E820h they should probably generate a fake e820
99 * map.
100 */
101 boot_params.alt_mem_k = oreg.ax;
102 }
103 }
104
105 static void detect_memory_88(void)
106 {
107 struct biosregs ireg, oreg;
108
109 initregs(&ireg);
110 ireg.ah = 0x88;
111 intcall(0x15, &ireg, &oreg);
112
113 boot_params.screen_info.ext_mem_k = oreg.ax;
114 }
115
116 void detect_memory(void)
117 {
118 detect_memory_e820();
119
120 detect_memory_e801();
121
122 detect_memory_88();
123 }