1 // SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
2 /******************************************************************************
4 * Module Name: tbxfroot - Find the root ACPI table (RSDT)
6 * Copyright (C) 2000 - 2023, Intel Corp.
8 *****************************************************************************/
10 #include <acpi/acpi.h>
14 #define _COMPONENT ACPI_TABLES
15 ACPI_MODULE_NAME("tbxfroot")
17 /*******************************************************************************
19 * FUNCTION: acpi_tb_get_rsdp_length
21 * PARAMETERS: rsdp - Pointer to RSDP
23 * RETURN: Table length
25 * DESCRIPTION: Get the length of the RSDP
27 ******************************************************************************/
28 u32 acpi_tb_get_rsdp_length(struct acpi_table_rsdp *rsdp)
31 if (!ACPI_VALIDATE_RSDP_SIG(rsdp->signature)) {
38 /* "Length" field is available if table version >= 2 */
40 if (rsdp->revision >= 2) {
41 return (rsdp->length);
43 return (ACPI_RSDP_CHECKSUM_LENGTH);
47 /*******************************************************************************
49 * FUNCTION: acpi_tb_validate_rsdp
51 * PARAMETERS: rsdp - Pointer to unvalidated RSDP
55 * DESCRIPTION: Validate the RSDP (ptr)
57 ******************************************************************************/
59 acpi_status acpi_tb_validate_rsdp(struct acpi_table_rsdp *rsdp)
63 * The signature and checksum must both be correct
65 * Note: Sometimes there exists more than one RSDP in memory; the valid
66 * RSDP has a valid checksum, all others have an invalid checksum.
68 if (!ACPI_VALIDATE_RSDP_SIG(rsdp->signature)) {
70 /* Nope, BAD Signature */
72 return (AE_BAD_SIGNATURE);
75 /* Check the standard checksum */
77 if (acpi_ut_checksum((u8 *)rsdp, ACPI_RSDP_CHECKSUM_LENGTH) != 0) {
78 return (AE_BAD_CHECKSUM);
81 /* Check extended checksum if table version >= 2 */
83 if ((rsdp->revision >= 2) &&
84 (acpi_ut_checksum((u8 *)rsdp, ACPI_RSDP_XCHECKSUM_LENGTH) != 0)) {
85 return (AE_BAD_CHECKSUM);
91 /*******************************************************************************
93 * FUNCTION: acpi_find_root_pointer
95 * PARAMETERS: table_address - Where the table pointer is returned
97 * RETURN: Status, RSDP physical address
99 * DESCRIPTION: Search lower 1Mbyte of memory for the root system descriptor
100 * pointer structure. If it is found, set *RSDP to point to it.
102 * NOTE1: The RSDP must be either in the first 1K of the Extended
103 * BIOS Data Area or between E0000 and FFFFF (From ACPI Spec.)
104 * Only a 32-bit physical address is necessary.
106 * NOTE2: This function is always available, regardless of the
107 * initialization state of the rest of ACPI.
109 ******************************************************************************/
111 acpi_status ACPI_INIT_FUNCTION
112 acpi_find_root_pointer(acpi_physical_address *table_address)
116 u32 physical_address;
117 u32 ebda_window_size;
119 ACPI_FUNCTION_TRACE(acpi_find_root_pointer);
121 /* 1a) Get the location of the Extended BIOS Data Area (EBDA) */
123 table_ptr = acpi_os_map_memory((acpi_physical_address)
124 ACPI_EBDA_PTR_LOCATION,
125 ACPI_EBDA_PTR_LENGTH);
128 "Could not map memory at 0x%8.8X for length %u",
129 ACPI_EBDA_PTR_LOCATION, ACPI_EBDA_PTR_LENGTH));
131 return_ACPI_STATUS(AE_NO_MEMORY);
134 ACPI_MOVE_16_TO_32(&physical_address, table_ptr);
136 /* Convert segment part to physical address */
138 physical_address <<= 4;
139 acpi_os_unmap_memory(table_ptr, ACPI_EBDA_PTR_LENGTH);
144 * Check that the EBDA pointer from memory is sane and does not point
145 * above valid low memory
147 if (physical_address > 0x400 && physical_address < 0xA0000) {
149 * Calculate the scan window size
150 * The EBDA is not guaranteed to be larger than a ki_b and in case
151 * that it is smaller, the scanning function would leave the low
152 * memory and continue to the VGA range.
154 ebda_window_size = ACPI_MIN(ACPI_EBDA_WINDOW_SIZE,
155 0xA0000 - physical_address);
158 * 1b) Search EBDA paragraphs
160 table_ptr = acpi_os_map_memory((acpi_physical_address)
165 "Could not map memory at 0x%8.8X for length %u",
166 physical_address, ebda_window_size));
168 return_ACPI_STATUS(AE_NO_MEMORY);
172 acpi_tb_scan_memory_for_rsdp(table_ptr, ebda_window_size);
173 acpi_os_unmap_memory(table_ptr, ebda_window_size);
177 /* Return the physical address */
180 (u32) ACPI_PTR_DIFF(mem_rover, table_ptr);
183 (acpi_physical_address)physical_address;
184 return_ACPI_STATUS(AE_OK);
189 * 2) Search upper memory: 16-byte boundaries in E0000h-FFFFFh
191 table_ptr = acpi_os_map_memory((acpi_physical_address)
192 ACPI_HI_RSDP_WINDOW_BASE,
193 ACPI_HI_RSDP_WINDOW_SIZE);
197 "Could not map memory at 0x%8.8X for length %u",
198 ACPI_HI_RSDP_WINDOW_BASE,
199 ACPI_HI_RSDP_WINDOW_SIZE));
201 return_ACPI_STATUS(AE_NO_MEMORY);
205 acpi_tb_scan_memory_for_rsdp(table_ptr, ACPI_HI_RSDP_WINDOW_SIZE);
206 acpi_os_unmap_memory(table_ptr, ACPI_HI_RSDP_WINDOW_SIZE);
210 /* Return the physical address */
212 physical_address = (u32)
213 (ACPI_HI_RSDP_WINDOW_BASE +
214 ACPI_PTR_DIFF(mem_rover, table_ptr));
216 *table_address = (acpi_physical_address)physical_address;
217 return_ACPI_STATUS(AE_OK);
220 /* A valid RSDP was not found */
222 ACPI_BIOS_ERROR((AE_INFO, "A valid RSDP was not found"));
223 return_ACPI_STATUS(AE_NOT_FOUND);
226 ACPI_EXPORT_SYMBOL_INIT(acpi_find_root_pointer)
228 /*******************************************************************************
230 * FUNCTION: acpi_tb_scan_memory_for_rsdp
232 * PARAMETERS: start_address - Starting pointer for search
233 * length - Maximum length to search
235 * RETURN: Pointer to the RSDP if found, otherwise NULL.
237 * DESCRIPTION: Search a block of memory for the RSDP signature
239 ******************************************************************************/
240 u8 *acpi_tb_scan_memory_for_rsdp(u8 *start_address, u32 length)
246 ACPI_FUNCTION_TRACE(tb_scan_memory_for_rsdp);
248 end_address = start_address + length;
250 /* Search from given start address for the requested length */
252 for (mem_rover = start_address; mem_rover < end_address;
253 mem_rover += ACPI_RSDP_SCAN_STEP) {
255 /* The RSDP signature and checksum must both be correct */
258 acpi_tb_validate_rsdp(ACPI_CAST_PTR
259 (struct acpi_table_rsdp, mem_rover));
260 if (ACPI_SUCCESS(status)) {
262 /* Sig and checksum valid, we have found a real RSDP */
264 ACPI_DEBUG_PRINT((ACPI_DB_INFO,
265 "RSDP located at physical address %p\n",
267 return_PTR(mem_rover);
270 /* No sig match or bad checksum, keep searching */
273 /* Searched entire block, no RSDP was found */
275 ACPI_DEBUG_PRINT((ACPI_DB_INFO,
276 "Searched entire block from %p, valid RSDP was not found\n",