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 #include <linux/kernel.h> 17 18 #define SMAP 0x534d4150 /* ASCII "SMAP" */ 19 20 static int detect_memory_e820(void) 21 { 22 int count = 0; 23 u32 next = 0; 24 u32 size, id; 25 u8 err; 26 struct e820entry *desc = boot_params.e820_map; 27 28 do { 29 size = sizeof(struct e820entry); 30 31 /* Important: %edx is clobbered by some BIOSes, 32 so it must be either used for the error output 33 or explicitly marked clobbered. */ 34 asm("int $0x15; setc %0" 35 : "=d" (err), "+b" (next), "=a" (id), "+c" (size), 36 "=m" (*desc) 37 : "D" (desc), "d" (SMAP), "a" (0xe820)); 38 39 /* BIOSes which terminate the chain with CF = 1 as opposed 40 to %ebx = 0 don't always report the SMAP signature on 41 the final, failing, probe. */ 42 if (err) 43 break; 44 45 /* Some BIOSes stop returning SMAP in the middle of 46 the search loop. We don't know exactly how the BIOS 47 screwed up the map at that point, we might have a 48 partial map, the full map, or complete garbage, so 49 just return failure. */ 50 if (id != SMAP) { 51 count = 0; 52 break; 53 } 54 55 count++; 56 desc++; 57 } while (next && count < ARRAY_SIZE(boot_params.e820_map)); 58 59 return boot_params.e820_entries = count; 60 } 61 62 static int detect_memory_e801(void) 63 { 64 u16 ax, bx, cx, dx; 65 u8 err; 66 67 bx = cx = dx = 0; 68 ax = 0xe801; 69 asm("stc; int $0x15; setc %0" 70 : "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx)); 71 72 if (err) 73 return -1; 74 75 /* Do we really need to do this? */ 76 if (cx || dx) { 77 ax = cx; 78 bx = dx; 79 } 80 81 if (ax > 15*1024) 82 return -1; /* Bogus! */ 83 84 /* This ignores memory above 16MB if we have a memory hole 85 there. If someone actually finds a machine with a memory 86 hole at 16MB and no support for 0E820h they should probably 87 generate a fake e820 map. */ 88 boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax; 89 90 return 0; 91 } 92 93 static int detect_memory_88(void) 94 { 95 u16 ax; 96 u8 err; 97 98 ax = 0x8800; 99 asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax)); 100 101 boot_params.screen_info.ext_mem_k = ax; 102 103 return -err; 104 } 105 106 int detect_memory(void) 107 { 108 int err = -1; 109 110 if (detect_memory_e820() > 0) 111 err = 0; 112 113 if (!detect_memory_e801()) 114 err = 0; 115 116 if (!detect_memory_88()) 117 err = 0; 118 119 return err; 120 } 121