1#include <linux/kernel.h>
 2#include <linux/init.h>
 3#include <linux/memblock.h>
 4
 5#include <asm/setup.h>
 6#include <asm/bios_ebda.h>
 7
 8#define BIOS_LOWMEM_KILOBYTES 0x413
 9
10/*
11 * The BIOS places the EBDA/XBDA at the top of conventional
12 * memory, and usually decreases the reported amount of
13 * conventional memory (int 0x12) too. This also contains a
14 * workaround for Dell systems that neglect to reserve EBDA.
15 * The same workaround also avoids a problem with the AMD768MPX
16 * chipset: reserve a page before VGA to prevent PCI prefetch
17 * into it (errata #56). Usually the page is reserved anyways,
18 * unless you have no PS/2 mouse plugged in.
19 */
20void __init reserve_ebda_region(void)
21{
22	unsigned int lowmem, ebda_addr;
23
24	/* To determine the position of the EBDA and the */
25	/* end of conventional memory, we need to look at */
26	/* the BIOS data area. In a paravirtual environment */
27	/* that area is absent. We'll just have to assume */
28	/* that the paravirt case can handle memory setup */
29	/* correctly, without our help. */
30	if (paravirt_enabled())
31		return;
32
33	/* end of low (conventional) memory */
34	lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
35	lowmem <<= 10;
36
37	/* start of EBDA area */
38	ebda_addr = get_bios_ebda();
39
40	/* Fixup: bios puts an EBDA in the top 64K segment */
41	/* of conventional memory, but does not adjust lowmem. */
42	if ((lowmem - ebda_addr) <= 0x10000)
43		lowmem = ebda_addr;
44
45	/* Fixup: bios does not report an EBDA at all. */
46	/* Some old Dells seem to need 4k anyhow (bugzilla 2990) */
47	if ((ebda_addr == 0) && (lowmem >= 0x9f000))
48		lowmem = 0x9f000;
49
50	/* Paranoia: should never happen, but... */
51	if ((lowmem == 0) || (lowmem >= 0x100000))
52		lowmem = 0x9f000;
53
54	/* reserve all memory between lowmem and the 1MB mark */
55	memblock_reserve(lowmem, 0x100000 - lowmem);
56}