1 /* -*- linux-c -*- ------------------------------------------------------- * 2 * 3 * Copyright (C) 1991, 1992 Linus Torvalds 4 * Copyright 2007 rPath, Inc. - All Rights Reserved 5 * 6 * This file is part of the Linux kernel, and is made available under 7 * the terms of the GNU General Public License version 2. 8 * 9 * ----------------------------------------------------------------------- */ 10 11 /* 12 * Memory detection code 13 */ 14 15 #include "boot.h" 16 17 #define SMAP 0x534d4150 /* ASCII "SMAP" */ 18 19 static int detect_memory_e820(void) 20 { 21 int count = 0; 22 u32 next = 0; 23 u32 size, id; 24 u8 err; 25 struct e820entry *desc = boot_params.e820_map; 26 27 do { 28 size = sizeof(struct e820entry); 29 30 /* Important: %edx is clobbered by some BIOSes, 31 so it must be either used for the error output 32 or explicitly marked clobbered. */ 33 asm("int $0x15; setc %0" 34 : "=d" (err), "+b" (next), "=a" (id), "+c" (size), 35 "=m" (*desc) 36 : "D" (desc), "d" (SMAP), "a" (0xe820)); 37 38 /* BIOSes which terminate the chain with CF = 1 as opposed 39 to %ebx = 0 don't always report the SMAP signature on 40 the final, failing, probe. */ 41 if (err) 42 break; 43 44 /* Some BIOSes stop returning SMAP in the middle of 45 the search loop. We don't know exactly how the BIOS 46 screwed up the map at that point, we might have a 47 partial map, the full map, or complete garbage, so 48 just return failure. */ 49 if (id != SMAP) { 50 count = 0; 51 break; 52 } 53 54 count++; 55 desc++; 56 } while (next && count < E820MAX); 57 58 return boot_params.e820_entries = count; 59 } 60 61 static int detect_memory_e801(void) 62 { 63 u16 ax, bx, cx, dx; 64 u8 err; 65 66 bx = cx = dx = 0; 67 ax = 0xe801; 68 asm("stc; int $0x15; setc %0" 69 : "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx)); 70 71 if (err) 72 return -1; 73 74 /* Do we really need to do this? */ 75 if (cx || dx) { 76 ax = cx; 77 bx = dx; 78 } 79 80 if (ax > 15*1024) 81 return -1; /* Bogus! */ 82 83 /* This ignores memory above 16MB if we have a memory hole 84 there. If someone actually finds a machine with a memory 85 hole at 16MB and no support for 0E820h they should probably 86 generate a fake e820 map. */ 87 boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax; 88 89 return 0; 90 } 91 92 static int detect_memory_88(void) 93 { 94 u16 ax; 95 u8 err; 96 97 ax = 0x8800; 98 asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax)); 99 100 boot_params.screen_info.ext_mem_k = ax; 101 102 return -err; 103 } 104 105 int detect_memory(void) 106 { 107 int err = -1; 108 109 if (detect_memory_e820() > 0) 110 err = 0; 111 112 if (!detect_memory_e801()) 113 err = 0; 114 115 if (!detect_memory_88()) 116 err = 0; 117 118 return err; 119 } 120