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(regs: &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(int_no: 0x15, ireg: &ireg, oreg: &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(regs: &ireg); |
77 | ireg.ax = 0xe801; |
78 | intcall(int_no: 0x15, ireg: &ireg, oreg: &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(regs: &ireg); |
110 | ireg.ah = 0x88; |
111 | intcall(int_no: 0x15, ireg: &ireg, oreg: &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 | } |
124 | |