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 struct e820_ext_entry { 21 struct e820entry std; 22 u32 ext_flags; 23 } __attribute__((packed)); 24 25 static int detect_memory_e820(void) 26 { 27 int count = 0; 28 u32 next = 0; 29 u32 size, id, edi; 30 u8 err; 31 struct e820entry *desc = boot_params.e820_map; 32 static struct e820_ext_entry buf; /* static so it is zeroed */ 33 34 /* 35 * Set this here so that if the BIOS doesn't change this field 36 * but still doesn't change %ecx, we're still okay... 37 */ 38 buf.ext_flags = 1; 39 40 do { 41 size = sizeof buf; 42 43 /* Important: %edx and %esi are clobbered by some BIOSes, 44 so they must be either used for the error output 45 or explicitly marked clobbered. Given that, assume there 46 is something out there clobbering %ebp and %edi, too. */ 47 asm("pushl %%ebp; int $0x15; popl %%ebp; setc %0" 48 : "=d" (err), "+b" (next), "=a" (id), "+c" (size), 49 "=D" (edi), "+m" (buf) 50 : "D" (&buf), "d" (SMAP), "a" (0xe820) 51 : "esi"); 52 53 /* BIOSes which terminate the chain with CF = 1 as opposed 54 to %ebx = 0 don't always report the SMAP signature on 55 the final, failing, probe. */ 56 if (err) 57 break; 58 59 /* Some BIOSes stop returning SMAP in the middle of 60 the search loop. We don't know exactly how the BIOS 61 screwed up the map at that point, we might have a 62 partial map, the full map, or complete garbage, so 63 just return failure. */ 64 if (id != SMAP) { 65 count = 0; 66 break; 67 } 68 69 /* ACPI 3.0 added the extended flags support. If bit 0 70 in the extended flags is zero, we're supposed to simply 71 ignore the entry -- a backwards incompatible change! */ 72 if (size > 20 && !(buf.ext_flags & 1)) 73 continue; 74 75 *desc++ = buf.std; 76 count++; 77 } while (next && count < ARRAY_SIZE(boot_params.e820_map)); 78 79 return boot_params.e820_entries = count; 80 } 81 82 static int detect_memory_e801(void) 83 { 84 u16 ax, bx, cx, dx; 85 u8 err; 86 87 bx = cx = dx = 0; 88 ax = 0xe801; 89 asm("stc; int $0x15; setc %0" 90 : "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx)); 91 92 if (err) 93 return -1; 94 95 /* Do we really need to do this? */ 96 if (cx || dx) { 97 ax = cx; 98 bx = dx; 99 } 100 101 if (ax > 15*1024) 102 return -1; /* Bogus! */ 103 104 /* This ignores memory above 16MB if we have a memory hole 105 there. If someone actually finds a machine with a memory 106 hole at 16MB and no support for 0E820h they should probably 107 generate a fake e820 map. */ 108 boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax; 109 110 return 0; 111 } 112 113 static int detect_memory_88(void) 114 { 115 u16 ax; 116 u8 err; 117 118 ax = 0x8800; 119 asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax)); 120 121 boot_params.screen_info.ext_mem_k = ax; 122 123 return -err; 124 } 125 126 int detect_memory(void) 127 { 128 int err = -1; 129 130 if (detect_memory_e820() > 0) 131 err = 0; 132 133 if (!detect_memory_e801()) 134 err = 0; 135 136 if (!detect_memory_88()) 137 err = 0; 138 139 return err; 140 } 141