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// SPDX-License-Identifier: GPL-2.0-only
/* -*- linux-c -*- ------------------------------------------------------- *
*
* Copyright (C) 1991, 1992 Linus Torvalds
* Copyright 2007 rPath, Inc. - All Rights Reserved
* Copyright 2009 Intel Corporation; author H. Peter Anvin
*
* ----------------------------------------------------------------------- */
/*
* Memory detection code
*/
#include "boot.h"
#define SMAP 0x534d4150 /* ASCII "SMAP" */
static void detect_memory_e820(void)
{
int count = 0;
struct biosregs ireg, oreg;
struct boot_e820_entry *desc = boot_params.e820_table;
static struct boot_e820_entry buf; /* static so it is zeroed */
initregs(&ireg);
ireg.ax = 0xe820;
ireg.cx = sizeof(buf);
ireg.edx = SMAP;
ireg.di = (size_t)&buf;
/*
* Note: at least one BIOS is known which assumes that the
* buffer pointed to by one e820 call is the same one as
* the previous call, and only changes modified fields. Therefore,
* we use a temporary buffer and copy the results entry by entry.
*
* This routine deliberately does not try to account for
* ACPI 3+ extended attributes. This is because there are
* BIOSes in the field which report zero for the valid bit for
* all ranges, and we don't currently make any use of the
* other attribute bits. Revisit this if we see the extended
* attribute bits deployed in a meaningful way in the future.
*/
do {
intcall(0x15, &ireg, &oreg);
ireg.ebx = oreg.ebx; /* for next iteration... */
/* 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 (oreg.eflags & X86_EFLAGS_CF)
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 (oreg.eax != SMAP) {
count = 0;
break;
}
*desc++ = buf;
count++;
} while (ireg.ebx && count < ARRAY_SIZE(boot_params.e820_table));
boot_params.e820_entries = count;
}
static void detect_memory_e801(void)
{
struct biosregs ireg, oreg;
initregs(&ireg);
ireg.ax = 0xe801;
intcall(0x15, &ireg, &oreg);
if (oreg.eflags & X86_EFLAGS_CF)
return;
/* Do we really need to do this? */
if (oreg.cx || oreg.dx) {
oreg.ax = oreg.cx;
oreg.bx = oreg.dx;
}
if (oreg.ax > 15*1024) {
return; /* Bogus! */
} else if (oreg.ax == 15*1024) {
boot_params.alt_mem_k = (oreg.bx << 6) + oreg.ax;
} else {
/*
* 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 = oreg.ax;
}
}
static void detect_memory_88(void)
{
struct biosregs ireg, oreg;
initregs(&ireg);
ireg.ah = 0x88;
intcall(0x15, &ireg, &oreg);
boot_params.screen_info.ext_mem_k = oreg.ax;
}
void detect_memory(void)
{
detect_memory_e820();
detect_memory_e801();
detect_memory_88();
}
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