feat: madt parsing

kernel/include/init/acpi.h

@@ -12,9 +12,6 @@ constexpr uint32_t fold_signature(const char (&text)[5]) {
          | static_cast<uint32_t>(static_cast<uint8_t>(text[3])) << 24;
 }
 
-// Values match the folded signature stored in sdt_header_t::signature. DSDT and
-// FACS are absent on purpose: they are reached through the FADT, not listed in
-// the RSDT/XSDT.
 enum class signature : uint32_t {
     fadt = fold_signature("FACP"),
     madt = fold_signature("APIC"),
@@ -24,7 +21,6 @@ enum class signature : uint32_t {
     ssdt = fold_signature("SSDT"),
 };
 
-// A folded signature, unfolded back into a null-terminated 4-character string.
 struct signature_text_t {
     char text[5];
 };
@@ -63,6 +59,8 @@ struct rsdp_t {
 } __attribute__((packed));
 static_assert(sizeof(rsdp_t) == 36);
 
+struct madt_t;
+
 struct Rsdp {
     explicit Rsdp(paddr_t rsdp_physical) : physical(rsdp_physical) {}
 
@@ -75,20 +73,33 @@ struct Rsdp {
         for (auto index = 0u; index < count; index++) {
             uint64_t table_physical = 0;
             memcpy(&table_physical, entries + index * entry_size, entry_size);
-            callback(paddr_t{table_physical});
+            dispatch(paddr_t{table_physical}.access<sdt_header_t>(), callback);
         }
     }
 
+private:
     template<typename Fn>
-    void find_table(signature sig, Fn&& callback) {
-        for_each_table([&](paddr_t table) {
-            if (table.access<sdt_header_t>()->signature == static_cast<uint32_t>(sig)) {
-                callback(table);
-            }
-        });
+    static void dispatch(const sdt_header_t* header, Fn&& fn) {
+#define ACPI_DISPATCH(signature_enum, TableType) \
+    case signature::signature_enum: \
+        if constexpr (requires { fn(static_cast<const TableType*>(nullptr)); }) { \
+            fn(reinterpret_cast<const TableType*>(header)); \
+            return; \
+        } \
+        break;
+
+        switch (static_cast<signature>(header->signature)) {
+            ACPI_DISPATCH(madt, madt_t)
+            default: break;
+        }
+
+#undef ACPI_DISPATCH
+
+        if constexpr (requires { fn(static_cast<const sdt_header_t*>(nullptr)); }) {
+            fn(header);
+        }
     }
 
-private:
     bool uses_xsdt() {
         return physical.access<rsdp_t>()->revision >= 2;
     }