// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
/******************************************************************************
*
* Module Name: tbxfroot - Find the root ACPI table (RSDT)
*
* Copyright (C) 2000 - 2025, Intel Corp.
*
*****************************************************************************/
#include <acpi/acpi.h>
#include "accommon.h"
#include "actables.h"
#define _COMPONENT ACPI_TABLES
ACPI_MODULE_NAME(
"tbxfroot")
/*******************************************************************************
*
* FUNCTION: acpi_tb_get_rsdp_length
*
* PARAMETERS: rsdp - Pointer to RSDP
*
* RETURN: Table length
*
* DESCRIPTION: Get the length of the RSDP
*
******************************************************************************/
u32 acpi_tb_get_rsdp_length(
struct acpi_table_rsdp *rsdp)
{
if (!ACPI_VALIDATE_RSDP_SIG(rsdp->signature)) {
/* BAD Signature */
return (0);
}
/* "Length" field is available if table version >= 2 */
if (rsdp->revision >= 2) {
return (rsdp->length);
}
else {
return (ACPI_RSDP_CHECKSUM_LENGTH);
}
}
/*******************************************************************************
*
* FUNCTION: acpi_tb_validate_rsdp
*
* PARAMETERS: rsdp - Pointer to unvalidated RSDP
*
* RETURN: Status
*
* DESCRIPTION: Validate the RSDP (ptr)
*
******************************************************************************/
acpi_status acpi_tb_validate_rsdp(
struct acpi_table_rsdp *rsdp)
{
/*
* The signature and checksum must both be correct
*
* Note: Sometimes there exists more than one RSDP in memory; the valid
* RSDP has a valid checksum, all others have an invalid checksum.
*/
if (!ACPI_VALIDATE_RSDP_SIG(rsdp->signature)) {
/* Nope, BAD Signature */
return (AE_BAD_SIGNATURE);
}
/* Check the standard checksum */
if (acpi_ut_checksum((u8 *)rsdp, ACPI_RSDP_CHECKSUM_LENGTH) != 0) {
return (AE_BAD_CHECKSUM);
}
/* Check extended checksum if table version >= 2 */
if ((rsdp->revision >= 2) &&
(acpi_ut_checksum((u8 *)rsdp, ACPI_RSDP_XCHECKSUM_LENGTH) != 0)) {
return (AE_BAD_CHECKSUM);
}
return (AE_OK);
}
/*******************************************************************************
*
* FUNCTION: acpi_find_root_pointer
*
* PARAMETERS: table_address - Where the table pointer is returned
*
* RETURN: Status, RSDP physical address
*
* DESCRIPTION: Search lower 1Mbyte of memory for the root system descriptor
* pointer structure. If it is found, set *RSDP to point to it.
*
* NOTE1: The RSDP must be either in the first 1K of the Extended
* BIOS Data Area or between E0000 and FFFFF (From ACPI Spec.)
* Only a 32-bit physical address is necessary.
*
* NOTE2: This function is always available, regardless of the
* initialization state of the rest of ACPI.
*
******************************************************************************/
acpi_status ACPI_INIT_FUNCTION
acpi_find_root_pointer(acpi_physical_address *table_address)
{
u8 *table_ptr;
u8 *mem_rover;
u32 physical_address;
u32 ebda_window_size;
ACPI_FUNCTION_TRACE(acpi_find_root_pointer);
/* 1a) Get the location of the Extended BIOS Data Area (EBDA) */
table_ptr = acpi_os_map_memory((acpi_physical_address)
ACPI_EBDA_PTR_LOCATION,
ACPI_EBDA_PTR_LENGTH);
if (!table_ptr) {
ACPI_ERROR((AE_INFO,
"Could not map memory at 0x%8.8X for length %u",
ACPI_EBDA_PTR_LOCATION, ACPI_EBDA_PTR_LENGTH));
return_ACPI_STATUS(AE_NO_MEMORY);
}
ACPI_MOVE_16_TO_32(&physical_address, table_ptr);
/* Convert segment part to physical address */
physical_address <<= 4;
acpi_os_unmap_memory(table_ptr, ACPI_EBDA_PTR_LENGTH);
/* EBDA present? */
/*
* Check that the EBDA pointer from memory is sane and does not point
* above valid low memory
*/
if (physical_address > 0x400 && physical_address < 0xA0000) {
/*
* Calculate the scan window size
* The EBDA is not guaranteed to be larger than a ki_b and in case
* that it is smaller, the scanning function would leave the low
* memory and continue to the VGA range.
*/
ebda_window_size = ACPI_MIN(ACPI_EBDA_WINDOW_SIZE,
0xA0000 - physical_address);
/*
* 1b) Search EBDA paragraphs
*/
table_ptr = acpi_os_map_memory((acpi_physical_address)
physical_address,
ebda_window_size);
if (!table_ptr) {
ACPI_ERROR((AE_INFO,
"Could not map memory at 0x%8.8X for length %u",
physical_address, ebda_window_size));
return_ACPI_STATUS(AE_NO_MEMORY);
}
mem_rover =
acpi_tb_scan_memory_for_rsdp(table_ptr, ebda_window_size);
acpi_os_unmap_memory(table_ptr, ebda_window_size);
if (mem_rover) {
/* Return the physical address */
physical_address +=
(u32) ACPI_PTR_DIFF(mem_rover, table_ptr);
*table_address =
(acpi_physical_address)physical_address;
return_ACPI_STATUS(AE_OK);
}
}
/*
* 2) Search upper memory: 16-byte boundaries in E0000h-FFFFFh
*/
table_ptr = acpi_os_map_memory((acpi_physical_address)
ACPI_HI_RSDP_WINDOW_BASE,
ACPI_HI_RSDP_WINDOW_SIZE);
if (!table_ptr) {
ACPI_ERROR((AE_INFO,
"Could not map memory at 0x%8.8X for length %u",
ACPI_HI_RSDP_WINDOW_BASE,
ACPI_HI_RSDP_WINDOW_SIZE));
return_ACPI_STATUS(AE_NO_MEMORY);
}
mem_rover =
acpi_tb_scan_memory_for_rsdp(table_ptr, ACPI_HI_RSDP_WINDOW_SIZE);
acpi_os_unmap_memory(table_ptr, ACPI_HI_RSDP_WINDOW_SIZE);
if (mem_rover) {
/* Return the physical address */
physical_address = (u32)
(ACPI_HI_RSDP_WINDOW_BASE +
ACPI_PTR_DIFF(mem_rover, table_ptr));
*table_address = (acpi_physical_address)physical_address;
return_ACPI_STATUS(AE_OK);
}
/* A valid RSDP was not found */
ACPI_BIOS_ERROR((AE_INFO,
"A valid RSDP was not found"));
return_ACPI_STATUS(AE_NOT_FOUND);
}
ACPI_EXPORT_SYMBOL_INIT(acpi_find_root_pointer)
/*******************************************************************************
*
* FUNCTION: acpi_tb_scan_memory_for_rsdp
*
* PARAMETERS: start_address - Starting pointer for search
* length - Maximum length to search
*
* RETURN: Pointer to the RSDP if found, otherwise NULL.
*
* DESCRIPTION: Search a block of memory for the RSDP signature
*
******************************************************************************/
u8 *acpi_tb_scan_memory_for_rsdp(u8 *start_address, u32 length)
{
acpi_status status;
u8 *mem_rover;
u8 *end_address;
ACPI_FUNCTION_TRACE(tb_scan_memory_for_rsdp);
end_address = start_address + length;
/* Search from given start address for the requested length */
for (mem_rover = start_address; mem_rover < end_address;
mem_rover += ACPI_RSDP_SCAN_STEP) {
/* The RSDP signature and checksum must both be correct */
status =
acpi_tb_validate_rsdp(ACPI_CAST_PTR
(
struct acpi_table_rsdp, mem_rover));
if (ACPI_SUCCESS(status)) {
/* Sig and checksum valid, we have found a real RSDP */
ACPI_DEBUG_PRINT((ACPI_DB_INFO,
"RSDP located at physical address %p\n",
mem_rover));
return_PTR(mem_rover);
}
/* No sig match or bad checksum, keep searching */
}
/* Searched entire block, no RSDP was found */
ACPI_DEBUG_PRINT((ACPI_DB_INFO,
"Searched entire block from %p, valid RSDP was not found\n",
start_address));
return_PTR(NULL);
}
