From 2abd22178923ec225c4426dbfae3737b0011ec25 Mon Sep 17 00:00:00 2001
From: Thomas Oltmann <thomas.oltmann.hhg@gmail.com>
Date: Wed, 8 Jul 2026 21:52:16 +0200
Subject: [PATCH] Utility to choose good IRQ numbers

---
 include/cpu.h           | 11 ++++++++++-
 include/x86_64/apic.h   |  2 ++
 src/x86_64/cpu.c        | 33 +++++++++++++++++++++++++++++++++
 src/x86_64/lapic.c      |  2 +-
 src/x86_64/ps2_driver.c | 15 +++++++++++----
 5 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/include/cpu.h b/include/cpu.h
index 60087c2..b22dc40 100644
--- a/include/cpu.h
+++ b/include/cpu.h
@@ -17,7 +17,6 @@ unsigned int cpu_get_core_id(void);
 void write_gs_base(uint64_t base);
 
 
-#define LINEBUF_SIZE 256
 struct cpu_info {
     // first member of struct is pointer to itself, for easier loading
     struct cpu_info* cpu_info;
@@ -35,4 +34,14 @@ static inline struct cpu_info *local_cpu_data(void) {
 
 void interrupt_handler_register(unsigned int vector, void (*handler)(void));
 
+/** Choose one of the 223 interrupt numbers available for Hardware IRQs.
+ *  This function is useful for drivers that can control the IRQ numbers they are assigned
+ *  (e.g. hardware using MSI, MSI-X or the IOAPIC).
+ *  Interrupt numbers are chosen based on a hash of the arguments given to the function.
+ *  This ensures evenly spread interrupt numbers, that are stable across
+ *  multiple boots, kernel changes, and different computers.
+ */
+unsigned int choose_irq_vector(const char *system_name,
+    uint64_t instance_idx, uint64_t subinstance_idx);
+
 #endif
diff --git a/include/x86_64/apic.h b/include/x86_64/apic.h
index be7ef74..473b1e7 100644
--- a/include/x86_64/apic.h
+++ b/include/x86_64/apic.h
@@ -4,6 +4,8 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+#define LAPIC_SPURIOUS_VECTOR_NUMBER 0xFF
+
 void lapic_init(void);
 unsigned lapic_get_id(void);
 void lapic_eoi(void);
diff --git a/src/x86_64/cpu.c b/src/x86_64/cpu.c
index 6277636..0e49ec0 100644
--- a/src/x86_64/cpu.c
+++ b/src/x86_64/cpu.c
@@ -620,3 +620,36 @@ void cpu_init_ap_1(uint8_t core_id) {
     main();
     PANIC("return from main?");
 }
+
+/* Fowler-Noll-Vo Hash Function (Alternate) */
+
+#define FNV32_PRIME        16777619u
+#define FNV32_OFFSET_BASIS 2166136261u
+
+static void
+hash32_fnv1a(uint32_t *hash, const void *d, unsigned n)
+{
+    const uint8_t *c = d;
+    uint32_t h = *hash;
+    for (unsigned i = 0; i < n; i++) {
+        h ^= *c;
+        h *= FNV32_PRIME;
+        c++;
+    }
+    *hash = h;
+}
+
+unsigned int choose_irq_vector(const char *system_name,
+    uint64_t instance_idx, uint64_t subinstance_idx)
+{
+    uint32_t hash = FNV32_OFFSET_BASIS;
+    hash32_fnv1a(&hash, system_name, strlen(system_name));
+    hash32_fnv1a(&hash, &instance_idx, sizeof instance_idx);
+    hash32_fnv1a(&hash, &subinstance_idx, sizeof subinstance_idx);
+    hash &= 0xFF;
+    // TODO this biases IRQ vectors into specific numbers, fix it
+    if (hash < 32) hash += 32;
+    if (hash == LAPIC_SPURIOUS_VECTOR_NUMBER) hash ^= 1;
+    return hash;
+}
+
diff --git a/src/x86_64/lapic.c b/src/x86_64/lapic.c
index 8dd43f8..5a39014 100644
--- a/src/x86_64/lapic.c
+++ b/src/x86_64/lapic.c
@@ -58,7 +58,7 @@ void lapic_init(void)
 {
     ASSERT((LAPIC_ADDR->lapic_version.value & 0xff) <= 0x15);
 
-    LAPIC_ADDR->spurious_vector.value = SPURIOUS_VECTOR_APIC_ENABLE | 0xff;
+    LAPIC_ADDR->spurious_vector.value = SPURIOUS_VECTOR_APIC_ENABLE | LAPIC_SPURIOUS_VECTOR_NUMBER;
     wbinvd();
 }
 
diff --git a/src/x86_64/ps2_driver.c b/src/x86_64/ps2_driver.c
index 34769cd..5dede0f 100644
--- a/src/x86_64/ps2_driver.c
+++ b/src/x86_64/ps2_driver.c
@@ -382,13 +382,20 @@ void ps2_init() {
     }
 
     /* register interrupt handlers */
-    interrupt_handler_register(101, port1_handler);
-    interrupt_handler_register(102, port2_handler);
+
+    unsigned port1_irq = choose_irq_vector("ps2", 0, 1);
+    unsigned port2_irq = choose_irq_vector("ps2", 0, 2);
+
+    printlinef("port1_irq = %d", port1_irq);
+    printlinef("port2_irq = %d", port2_irq);
+
+    interrupt_handler_register(port1_irq, port1_handler);
+    interrupt_handler_register(port2_irq, port2_handler);
 
     bool success;
-    success = ioapic_configure_irq(1, 101 | IORED_DELIVERY_NORMAL | ((uint64_t)lapic_get_id() << IORED_DESTINATION_SHIFT));
+    success = ioapic_configure_irq(1, port1_irq | IORED_DELIVERY_NORMAL | ((uint64_t)lapic_get_id() << IORED_DESTINATION_SHIFT));
     ASSERT(success);
-    success = ioapic_configure_irq(12, 102 | IORED_DELIVERY_NORMAL | ((uint64_t)lapic_get_id() << IORED_DESTINATION_SHIFT));
+    success = ioapic_configure_irq(12, port2_irq | IORED_DELIVERY_NORMAL | ((uint64_t)lapic_get_id() << IORED_DESTINATION_SHIFT));
     ASSERT(success);
 
     ps2_cmd_with_data(CMD_TO_CNTRL_OUTPUT, 0x03);