Handout

kernel/arch/acpi.cc

@@ -0,0 +1,146 @@
+#include "acpi.h"
+
+#include "../debug/output.h"
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Warray-bounds"
+
+namespace ACPI {
+
+static RSDP *rsdp = nullptr;
+static RSDT *rsdt = nullptr;
+static XSDT *xsdt = nullptr;
+
+constexpr const char *RSDP_SIGNATURE = "RSD PTR ";
+
+static int checksum(const void *pos, unsigned len) {
+	const uint8_t *mem = reinterpret_cast<const uint8_t *>(pos);
+	uint8_t sum = 0;
+	for (unsigned i = 0; i < len; i++) {
+		sum += mem[i];
+	}
+
+	return sum;
+}
+
+static const RSDP *findRSDP(const void *pos, unsigned len) {
+	/* since the RSDP is 16-Byte aligned, we only need to check
+	every second 64bit memory block */
+	for (unsigned block = 0; block < len / 8; block += 2) {
+		const uint64_t *mem = reinterpret_cast<const uint64_t *>(pos) + block;
+		if (*mem == *reinterpret_cast<const uint64_t *>(RSDP_SIGNATURE)) {
+			const RSDP *rsdp = reinterpret_cast<const RSDP *>(mem);
+			/* ACPI Specification Revision 4.0a: 5.2.5.3*/
+			if ((rsdp->revision == 0 && checksum(mem, 20) == 0) ||
+				(rsdp->length > 20 && checksum(mem, rsdp->length) == 0)) {
+				return rsdp;
+			}
+		}
+	}
+	return 0;
+}
+
+bool init() {
+	/* ACPI Specification Revision 4.0a:
+	 * 5.2.5.1 Finding the RSDP on IA-PC Systems
+	 * OSPM finds the Root System Description Pointer (RSDP) structure by
+	 * searching physical memory ranges on 16-byte boundaries for a valid
+	 * Root System Description Pointer structure signature and checksum
+	 * match as follows:
+	 * * The first 1 KB of the Extended BIOS Data Area (EBDA). For EISA or
+	 *   MCA systems, the EBDA can be found in the two-byte location 40:0Eh
+	 *   on the BIOS data area.
+	 * * The BIOS read-only memory space between 0E0000h and 0FFFFFh.
+	 */
+	const uintptr_t ebda =
+		static_cast<uintptr_t>(*reinterpret_cast<uint32_t *>(0x40e));
+	const RSDP *rsdp = findRSDP(reinterpret_cast<void *>(ebda), 1024);
+	if (rsdp == nullptr) {
+		rsdp = findRSDP(reinterpret_cast<void *>(0xe0000), 0xfffff - 0xe0000);
+	}
+
+	if (rsdp == nullptr) {
+		DBG_VERBOSE << "No ACPI!" << endl;
+		return false;
+	}
+	rsdt = reinterpret_cast<RSDT *>(static_cast<uintptr_t>(rsdp->rsdtaddress));
+
+	/* If the XSDT is present we must use it; see:
+	 * ACPI Specification Revision 4.0a:
+	 * "An ACPI-compatible OS must use the XSDT if present."
+	 */
+	if (rsdp->revision != 0 && rsdp->length >= 36) {
+		xsdt = reinterpret_cast<XSDT *>(rsdp->xsdtaddress);
+	}
+	DBG_VERBOSE << "ACPI revision " << rsdp->revision << endl;
+	for (unsigned i = 0; i != count(); ++i) {
+		SDTH *sdt = get(i);
+		if (sdt != nullptr) {
+			char *c = reinterpret_cast<char *>(&sdt->signature);
+			DBG_VERBOSE << i << ". " << c[0] << c[1] << c[2] << c[3] << " @ "
+						<< reinterpret_cast<void *>(sdt) << endl;
+		}
+	}
+	return true;
+}
+
+unsigned count() {
+	if (xsdt != nullptr) {
+		return (xsdt->length - 36) / 8;
+	} else if (rsdt != nullptr) {
+		return (rsdt->length - 36) / 4;
+	} else {
+		return 0;
+	}
+}
+
+SDTH *get(unsigned num) {
+	if (xsdt != nullptr) {
+		SDTH *entry = reinterpret_cast<SDTH *>(xsdt->entries[num]);
+		if (checksum(entry, entry->length) == 0) {
+			return entry;
+		}
+	} else if (rsdt != nullptr) {
+		SDTH *entry = reinterpret_cast<SDTH *>(
+			static_cast<uintptr_t>(rsdt->entries[num]));
+		if (checksum(entry, entry->length) == 0) {
+			return entry;
+		}
+	}
+	return 0;
+}
+
+SDTH *get(char a, char b, char c, char d) {
+	union {
+		char signature[4];
+		uint32_t value;
+	};
+	signature[0] = a;
+	signature[1] = b;
+	signature[2] = c;
+	signature[3] = d;
+
+	if (xsdt != nullptr) {
+		for (unsigned i = 0; i < count(); i++) {
+			SDTH *entry = reinterpret_cast<SDTH *>(xsdt->entries[i]);
+			if (entry->signature == value &&
+				checksum(entry, entry->length) == 0) {
+				return entry;
+			}
+		}
+	} else if (rsdt != nullptr) {
+		for (unsigned i = 0; i < count(); i++) {
+			SDTH *entry = reinterpret_cast<SDTH *>(
+				static_cast<uintptr_t>(rsdt->entries[i]));
+			if (entry->signature == value &&
+				checksum(entry, entry->length) == 0) {
+				return entry;
+			}
+		}
+	}
+	return 0;
+}
+
+int revision() { return rsdp != nullptr ? rsdp->revision : -1; }
+
+}  // namespace ACPI