stos/amd64: irqchip: Detect and disable i8259s

Signed-off-by: Chloe M. <chloe@mensia.org>

paw/stos/arch/amd64/platform/board.c

@@ -8,9 +8,14 @@
 
 #include <hal/board.h>
 #include <machine/hpet.h>
+#include <machine/irqchip.h>
 
 VOID
 HalBoardInit(VOID)
 {
+    /* Initialize HPET */
     MdHpetInit();
+
+    /* Initialize IRQ chips */
+    MdIrqChipInit();
 }

paw/stos/arch/amd64/platform/irqchip.c

@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: IRQ chip management
+ * Author:      Chloe M.
+ */
+
+#include <drivers/acpi/tables.h>
+#include <drivers/acpi/acpi.h>
+#include <machine/irqchip.h>
+#include <machine/pio.h>
+#include <ke/knot.h>
+#include <ex/trace.h>
+
+/* PIC data ports */
+#define PIC_MASTER_DATA 0x21
+#define PIC_SLAVE_DATA  0xA1
+
+#define DTRACE(Fmt, ...) \
+    TRACE("[ IRQCHIP ]: " Fmt, ##__VA_ARGS__)
+
+/* Set if dual i8259 is present */
+#define MADT_PCAT_COMPAT BIT(0)
+
+VOID
+MdIrqChipInit(VOID)
+{
+    ACPI_MADT *Madt;
+
+    Madt = AcpiQuery("APIC");
+    if (Madt == NULL) {
+        KeKnot(
+            KNOT_UNBOUND_RSRC,
+            "could not locate ACPI MADT\n"
+        );
+    }
+
+    /*
+     * If we have a dual-i8259 configuration present on the
+     * machine, we'll want to disable it so it doesn't mess
+     * up Local APIC operation and such.
+     */
+    if (ISSET(Madt->Flags, MADT_PCAT_COMPAT)) {
+        DTRACE("detected dual i8259; disabling...\n");
+        MdOutb(PIC_MASTER_DATA, 0xFF);
+        MdOutb(PIC_SLAVE_DATA, 0xFF);
+    }
+}