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97873a3d | 1 | // SPDX-License-Identifier: GPL-2.0-only |
449f2ab9 PA |
2 | /* -*- linux-c -*- ------------------------------------------------------- * |
3 | * | |
4 | * Copyright (C) 1991, 1992 Linus Torvalds | |
5 | * Copyright 2007 rPath, Inc. - All Rights Reserved | |
c549e71d | 6 | * Copyright 2009 Intel Corporation; author H. Peter Anvin |
449f2ab9 | 7 | * |
449f2ab9 PA |
8 | * ----------------------------------------------------------------------- */ |
9 | ||
10 | /* | |
449f2ab9 PA |
11 | * Memory detection code |
12 | */ | |
13 | ||
14 | #include "boot.h" | |
15 | ||
16 | #define SMAP 0x534d4150 /* ASCII "SMAP" */ | |
17 | ||
e8eeb3c8 | 18 | static void detect_memory_e820(void) |
449f2ab9 | 19 | { |
2efa33f8 | 20 | int count = 0; |
df7699c5 | 21 | struct biosregs ireg, oreg; |
7410aa1c IM |
22 | struct boot_e820_entry *desc = boot_params.e820_table; |
23 | static struct boot_e820_entry buf; /* static so it is zeroed */ | |
449f2ab9 | 24 | |
df7699c5 PA |
25 | initregs(&ireg); |
26 | ireg.ax = 0xe820; | |
0e96f31e | 27 | ireg.cx = sizeof(buf); |
df7699c5 PA |
28 | ireg.edx = SMAP; |
29 | ireg.di = (size_t)&buf; | |
30 | ||
cd670599 | 31 | /* |
bca23dba PA |
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. | |
cd670599 | 43 | */ |
cd670599 | 44 | |
449f2ab9 | 45 | do { |
df7699c5 PA |
46 | intcall(0x15, &ireg, &oreg); |
47 | ireg.ebx = oreg.ebx; /* for next iteration... */ | |
449f2ab9 | 48 | |
829157be PA |
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. */ | |
df7699c5 | 52 | if (oreg.eflags & X86_EFLAGS_CF) |
829157be PA |
53 | break; |
54 | ||
2efa33f8 PA |
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. */ | |
df7699c5 | 60 | if (oreg.eax != SMAP) { |
2efa33f8 | 61 | count = 0; |
449f2ab9 | 62 | break; |
2efa33f8 | 63 | } |
449f2ab9 | 64 | |
bca23dba | 65 | *desc++ = buf; |
2efa33f8 | 66 | count++; |
61a50101 | 67 | } while (ireg.ebx && count < ARRAY_SIZE(boot_params.e820_table)); |
449f2ab9 | 68 | |
e8eeb3c8 | 69 | boot_params.e820_entries = count; |
449f2ab9 PA |
70 | } |
71 | ||
e8eeb3c8 | 72 | static void detect_memory_e801(void) |
449f2ab9 | 73 | { |
df7699c5 | 74 | struct biosregs ireg, oreg; |
449f2ab9 | 75 | |
df7699c5 PA |
76 | initregs(&ireg); |
77 | ireg.ax = 0xe801; | |
78 | intcall(0x15, &ireg, &oreg); | |
449f2ab9 | 79 | |
df7699c5 | 80 | if (oreg.eflags & X86_EFLAGS_CF) |
e8eeb3c8 | 81 | return; |
449f2ab9 PA |
82 | |
83 | /* Do we really need to do this? */ | |
df7699c5 PA |
84 | if (oreg.cx || oreg.dx) { |
85 | oreg.ax = oreg.cx; | |
86 | oreg.bx = oreg.dx; | |
449f2ab9 PA |
87 | } |
88 | ||
df7699c5 | 89 | if (oreg.ax > 15*1024) { |
e8eeb3c8 | 90 | return; /* Bogus! */ |
df7699c5 | 91 | } else if (oreg.ax == 15*1024) { |
39b68976 | 92 | boot_params.alt_mem_k = (oreg.bx << 6) + oreg.ax; |
df7699c5 PA |
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 | } | |
449f2ab9 PA |
103 | } |
104 | ||
e8eeb3c8 | 105 | static void detect_memory_88(void) |
449f2ab9 | 106 | { |
df7699c5 | 107 | struct biosregs ireg, oreg; |
449f2ab9 | 108 | |
df7699c5 PA |
109 | initregs(&ireg); |
110 | ireg.ah = 0x88; | |
111 | intcall(0x15, &ireg, &oreg); | |
449f2ab9 | 112 | |
df7699c5 | 113 | boot_params.screen_info.ext_mem_k = oreg.ax; |
449f2ab9 PA |
114 | } |
115 | ||
e8eeb3c8 | 116 | void detect_memory(void) |
449f2ab9 | 117 | { |
e8eeb3c8 | 118 | detect_memory_e820(); |
2efa33f8 | 119 | |
e8eeb3c8 | 120 | detect_memory_e801(); |
449f2ab9 | 121 | |
e8eeb3c8 | 122 | detect_memory_88(); |
449f2ab9 | 123 | } |