linux/arch/x86/boot/memory.c
H. Peter Anvin 829157be59 x86: handle BIOSes which terminate e820 with CF=1 and no SMAP
The proper way to terminate the e820 chain is with %ebx == 0 on the
last legitimate memory block.  However, several BIOSes don't do that
and instead return error (CF = 1) when trying to read off the end of
the list.  For this error return, %eax doesn't necessarily return the
SMAP signature -- correctly so, since %ah should contain an error code
in this case.

To deal with some particularly broken BIOSes, we clear the entire e820
chain if the SMAP signature is missing in the middle, indicating a
plain insane e820 implementation.  However, we need to make the test
for CF = 1 before the SMAP check.

This fixes at least one HP laptop (nc6400) for which none of the
memory-probing methods (e820, e801, 88) functioned fully according to
spec.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-02-26 12:55:52 +01:00

122 lines
2.5 KiB
C

/* -*- linux-c -*- ------------------------------------------------------- *
*
* Copyright (C) 1991, 1992 Linus Torvalds
* Copyright 2007 rPath, Inc. - All Rights Reserved
*
* This file is part of the Linux kernel, and is made available under
* the terms of the GNU General Public License version 2.
*
* ----------------------------------------------------------------------- */
/*
* arch/i386/boot/memory.c
*
* Memory detection code
*/
#include "boot.h"
#define SMAP 0x534d4150 /* ASCII "SMAP" */
static int detect_memory_e820(void)
{
int count = 0;
u32 next = 0;
u32 size, id;
u8 err;
struct e820entry *desc = boot_params.e820_map;
do {
size = sizeof(struct e820entry);
/* Important: %edx is clobbered by some BIOSes,
so it must be either used for the error output
or explicitly marked clobbered. */
asm("int $0x15; setc %0"
: "=d" (err), "+b" (next), "=a" (id), "+c" (size),
"=m" (*desc)
: "D" (desc), "d" (SMAP), "a" (0xe820));
/* BIOSes which terminate the chain with CF = 1 as opposed
to %ebx = 0 don't always report the SMAP signature on
the final, failing, probe. */
if (err)
break;
/* Some BIOSes stop returning SMAP in the middle of
the search loop. We don't know exactly how the BIOS
screwed up the map at that point, we might have a
partial map, the full map, or complete garbage, so
just return failure. */
if (id != SMAP) {
count = 0;
break;
}
count++;
desc++;
} while (next && count < E820MAX);
return boot_params.e820_entries = count;
}
static int detect_memory_e801(void)
{
u16 ax, bx, cx, dx;
u8 err;
bx = cx = dx = 0;
ax = 0xe801;
asm("stc; int $0x15; setc %0"
: "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx));
if (err)
return -1;
/* Do we really need to do this? */
if (cx || dx) {
ax = cx;
bx = dx;
}
if (ax > 15*1024)
return -1; /* Bogus! */
/* This ignores memory above 16MB if we have a memory hole
there. If someone actually finds a machine with a memory
hole at 16MB and no support for 0E820h they should probably
generate a fake e820 map. */
boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax;
return 0;
}
static int detect_memory_88(void)
{
u16 ax;
u8 err;
ax = 0x8800;
asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax));
boot_params.screen_info.ext_mem_k = ax;
return -err;
}
int detect_memory(void)
{
int err = -1;
if (detect_memory_e820() > 0)
err = 0;
if (!detect_memory_e801())
err = 0;
if (!detect_memory_88())
err = 0;
return err;
}