// 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);
}