[PATCH v9 4/8] x86/boot: Add bios_get_rsdp_addr() to search RSDP in memory

Chao Fan
2018-10-17T10:20:08Z

Imitate acpi_find_root_pointer() and acpi_tb_scan_memory_for_rsdp()
to search RSDP table pointer in memory. This function only works
when RSDP not found in EFI table.

Signed-off-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
---
arch/x86/boot/compressed/acpitb.c | 106 ++++++++++++++++++++++++++++++
1 file changed, 106 insertions(+)

diff --git a/arch/x86/boot/compressed/acpitb.c b/arch/x86/boot/compressed/acpitb.c
index 56b54b0e0889..50fa65cf824d 100644
--- a/arch/x86/boot/compressed/acpitb.c
+++ b/arch/x86/boot/compressed/acpitb.c
@@ -94,3 +94,109 @@ static void efi_get_rsdp_addr(acpi_physical_address *rsdp_addr)
}
#endif
}
+
+static u8 compute_checksum(u8 *buffer, u32 length)
+{
+ u8 sum = 0;
+ u8 *end = buffer + length;
+
+ while (buffer < end)
+ sum = (u8)(sum + *(buffer++));
+
+ return sum;
+}
+
+/*
+ * Used to search a block of memory for the RSDP signature.
+ * Return Pointer to the RSDP if found, otherwise NULL.
+ * Based on acpi_tb_scan_memory_for_rsdp().
+ */
+static u8 *scan_mem_for_rsdp(u8 *start, u32 length)
+{
+ struct acpi_table_rsdp *rsdp;
+ u8 *end;
+ u8 *rover;
+
+ end = start + length;
+
+ /* Search from given start address for the requested length */
+ for (rover = start; rover < end; rover += ACPI_RSDP_SCAN_STEP) {
+ /*
+ * The RSDP 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.
+ */
+ rsdp = (struct acpi_table_rsdp *)rover;
+
+ /* Nope, BAD Signature */
+ if (!ACPI_VALIDATE_RSDP_SIG(rsdp->signature))
+ continue;
+
+ /* Check the standard checksum */
+ if (compute_checksum((u8 *) rsdp, ACPI_RSDP_CHECKSUM_LENGTH))
+ continue;
+
+ /* Check extended checksum if table version >= 2 */
+ if ((rsdp->revision >= 2) &&
+ (compute_checksum((u8 *) rsdp, ACPI_RSDP_XCHECKSUM_LENGTH)))
+ continue;
+
+ /* Sig and checksum valid, we have found a real RSDP */
+ return rover;
+ }
+ return NULL;
+}
+
+/*
+ * Used to search RSDP physical address.
+ * Based on acpi_find_root_pointer(). Since only use physical address
+ * in this period, so there is no need to do the memory map jobs.
+ */
+static void bios_get_rsdp_addr(acpi_physical_address *rsdp_addr)
+{
+ struct acpi_table_rsdp *rsdp;
+ u8 *table_ptr;
+ u8 *mem_rover;
+ u32 address;
+
+ /*
+ * Get the location of the Extended BIOS Data Area (EBDA)
+ * Since we use physical address directely, so
+ * acpi_os_map_memory() and acpi_os_unmap_memory() are
+ * not needed here.
+ */
+ table_ptr = (u8 *)ACPI_EBDA_PTR_LOCATION;
+ *(u32 *)(void *)&address = *(u16 *)(void *)table_ptr;
+ address <<= 4;
+ table_ptr = (u8 *)address;
+
+ /*
+ * Search EBDA paragraphs (EBDA is required to be a minimum of
+ * 1K length)
+ */
+ if (address > 0x400) {
+ mem_rover = scan_mem_for_rsdp(table_ptr, ACPI_EBDA_WINDOW_SIZE);
+
+ if (mem_rover) {
+ address += (u32)ACPI_PTR_DIFF(mem_rover, table_ptr);
+ *rsdp_addr = (acpi_physical_address)address;
+ return;
+ }
+ }
+
+ table_ptr = (u8 *)ACPI_HI_RSDP_WINDOW_BASE;
+ mem_rover = scan_mem_for_rsdp(table_ptr, ACPI_HI_RSDP_WINDOW_SIZE);
+
+ /*
+ * Search upper memory: 16-byte boundaries in E0000h-FFFFFh
+ * Since we use physical address directely, so
+ * acpi_os_map_memory() and acpi_os_unmap_memory() are
+ * not needed here.
+ */
+ if (mem_rover) {
+ address = (u32)(ACPI_HI_RSDP_WINDOW_BASE +
+ ACPI_PTR_DIFF(mem_rover, table_ptr));
+ *rsdp_addr = (acpi_physical_address)address;
+ }
+}
--
2.17.2