release/src-rt-6.x.4708/linux/linux-2.6.36/arch/x86/kernel/head.c

   1 #include <linux/kernel.h>
   2 #include <linux/init.h>
   3
   4 #include <asm/setup.h>
   5 #include <asm/bios_ebda.h>
   6
   7 #define BIOS_LOWMEM_KILOBYTES 0x413
   8
   9 void __init reserve_ebda_region(void)
  10 {
  11         unsigned int lowmem, ebda_addr;
  12
  13         /* To determine the position of the EBDA and the */
  14         /* end of conventional memory, we need to look at */
  15         /* the BIOS data area. In a paravirtual environment */
  16         /* that area is absent. We'll just have to assume */
  17         /* that the paravirt case can handle memory setup */
  18         /* correctly, without our help. */
  19         if (paravirt_enabled())
  20                 return;
  21
  22         /* end of low (conventional) memory */
  23         lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
  24         lowmem <<= 10;
  25
  26         /* start of EBDA area */
  27         ebda_addr = get_bios_ebda();
  28
  29         /* Fixup: bios puts an EBDA in the top 64K segment */
  30         /* of conventional memory, but does not adjust lowmem. */
  31         if ((lowmem - ebda_addr) <= 0x10000)
  32                 lowmem = ebda_addr;
  33
  34         /* Fixup: bios does not report an EBDA at all. */
  35         /* Some old Dells seem to need 4k anyhow (bugzilla 2990) */
  36         if ((ebda_addr == 0) && (lowmem >= 0x9f000))
  37                 lowmem = 0x9f000;
  38
  39         /* Paranoia: should never happen, but... */
  40         if ((lowmem == 0) || (lowmem >= 0x100000))
  41                 lowmem = 0x9f000;
  42
  43         /* reserve all memory between lowmem and the 1MB mark */
  44         reserve_early_overlap_ok(lowmem, 0x100000, "BIOS reserved");
  45 }