src/arch/x86/ebda.c

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2
   3 #include <acpi/acpi.h>
   4 #include <bootstate.h>
   5 #include <commonlib/endian.h>
   6 #include <types.h>
   7
   8 #define X86_BDA_SIZE            0x200
   9 #define X86_BDA_BASE            ((void *)0x400)
  10 #define X86_EBDA_SEGMENT        ((void *)0x40e)
  11 #define X86_EBDA_LOWMEM         ((void *)0x413)
  12
  13 #define DEFAULT_EBDA_LOWMEM     (1024 << 10)
  14 #define DEFAULT_EBDA_SEGMENT    0xF600
  15 #define DEFAULT_EBDA_SIZE       0x400
  16
  17
  18 static void *get_ebda_start(void)
  19 {
  20         return (void *)((uintptr_t)DEFAULT_EBDA_SEGMENT << 4);
  21 }
  22
  23 /*
  24  * EBDA area is representing a 1KB memory area just below
  25  * the top of conventional memory (below 1MB)
  26  */
  27
  28 static void setup_ebda(u32 low_memory_size, u16 ebda_segment, u16 ebda_size)
  29 {
  30         u16 low_memory_kb;
  31         u16 ebda_kb;
  32         void *ebda;
  33
  34         if (!low_memory_size || !ebda_segment || !ebda_size)
  35                 return;
  36
  37         low_memory_kb = low_memory_size >> 10;
  38         ebda_kb = ebda_size >> 10;
  39         ebda = get_ebda_start();
  40
  41         /* clear BIOS DATA AREA */
  42         zero_n(X86_BDA_BASE, X86_BDA_SIZE);
  43
  44         /* Avoid unaligned write16() since it's undefined behavior */
  45         write_le16(X86_EBDA_LOWMEM, low_memory_kb);
  46         write_le16(X86_EBDA_SEGMENT, ebda_segment);
  47
  48         /* Set up EBDA */
  49         zero_n(ebda, ebda_size);
  50         write_le16(ebda, ebda_kb);
  51 }
  52
  53 static void setup_default_ebda(void *unused)
  54 {
  55         if (acpi_is_wakeup_s3())
  56                 return;
  57
  58         setup_ebda(DEFAULT_EBDA_LOWMEM,
  59                    DEFAULT_EBDA_SEGMENT,
  60                    DEFAULT_EBDA_SIZE);
  61 }
  62
  63 /* Ensure EBDA is prepared before Option ROMs. */
  64 BOOT_STATE_INIT_ENTRY(BS_DEV_INIT, BS_ON_ENTRY, setup_default_ebda, NULL);