56 lines
1.8 KiB
C
56 lines
1.8 KiB
C
#include <linux/kernel.h>
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#include <linux/init.h>
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#include <asm/setup.h>
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#include <asm/bios_ebda.h>
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#define BIOS_LOWMEM_KILOBYTES 0x413
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/*
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* The BIOS places the EBDA/XBDA at the top of conventional
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* memory, and usually decreases the reported amount of
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* conventional memory (int 0x12) too. This also contains a
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* workaround for Dell systems that neglect to reserve EBDA.
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* The same workaround also avoids a problem with the AMD768MPX
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* chipset: reserve a page before VGA to prevent PCI prefetch
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* into it (errata #56). Usually the page is reserved anyways,
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* unless you have no PS/2 mouse plugged in.
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*/
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void __init reserve_ebda_region(void)
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{
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unsigned int lowmem, ebda_addr;
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/* To determine the position of the EBDA and the */
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/* end of conventional memory, we need to look at */
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/* the BIOS data area. In a paravirtual environment */
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/* that area is absent. We'll just have to assume */
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/* that the paravirt case can handle memory setup */
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/* correctly, without our help. */
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if (paravirt_enabled())
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return;
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/* end of low (conventional) memory */
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lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
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lowmem <<= 10;
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/* start of EBDA area */
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ebda_addr = get_bios_ebda();
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/* Fixup: bios puts an EBDA in the top 64K segment */
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/* of conventional memory, but does not adjust lowmem. */
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if ((lowmem - ebda_addr) <= 0x10000)
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lowmem = ebda_addr;
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/* Fixup: bios does not report an EBDA at all. */
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/* Some old Dells seem to need 4k anyhow (bugzilla 2990) */
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if ((ebda_addr == 0) && (lowmem >= 0x9f000))
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lowmem = 0x9f000;
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/* Paranoia: should never happen, but... */
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if ((lowmem == 0) || (lowmem >= 0x100000))
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lowmem = 0x9f000;
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/* reserve all memory between lowmem and the 1MB mark */
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reserve_early_overlap_ok(lowmem, 0x100000, "BIOS reserved");
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}
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