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 static void *get_ebda_start(void)
  14 {
  15         return (void *)((uintptr_t)CONFIG_DEFAULT_EBDA_SEGMENT << 4);
  16 }
  17
  18 /*
  19  * EBDA area is representing a 1KB memory area just below
  20  * the top of conventional memory (below 1MB)
  21  */
  22
  23 static void setup_ebda(u32 low_memory_size, u16 ebda_segment, u16 ebda_size)
  24 {
  25         u16 low_memory_kb;
  26         u16 ebda_kb;
  27         void *ebda;
  28
  29         if (!low_memory_size || !ebda_segment || !ebda_size)
  30                 return;
  31
  32         low_memory_kb = low_memory_size >> 10;
  33         ebda_kb = ebda_size >> 10;
  34         ebda = get_ebda_start();
  35
  36         /* clear BIOS DATA AREA */
  37         zero_n(X86_BDA_BASE, X86_BDA_SIZE);
  38
  39         /* Avoid unaligned write16() since it's undefined behavior */
  40         write_le16(X86_EBDA_LOWMEM, low_memory_kb);
  41         write_le16(X86_EBDA_SEGMENT, ebda_segment);
  42
  43         /* Set up EBDA */
  44         zero_n(ebda, ebda_size);
  45         write_le16(ebda, ebda_kb);
  46 }
  47
  48 static void setup_default_ebda(void *unused)
  49 {
  50         if (acpi_is_wakeup_s3())
  51                 return;
  52
  53         setup_ebda(CONFIG_DEFAULT_EBDA_LOWMEM,
  54                    CONFIG_DEFAULT_EBDA_SEGMENT,
  55                    CONFIG_DEFAULT_EBDA_SIZE);
  56 }
  57
  58 /* Ensure EBDA is prepared before Option ROMs. */
  59 BOOT_STATE_INIT_ENTRY(BS_DEV_INIT, BS_ON_ENTRY, setup_default_ebda, NULL);