From abff6e2191b8021b46ba8e8633b49b30e978919e Mon Sep 17 00:00:00 2001
From: kudasai <47227786+kudasaixc@users.noreply.github.com>
Date: Fri, 3 Jul 2026 18:54:22 +0200
Subject: [PATCH] fix(pic): unmask cascade IRQ2 when enabling a slave IRQ

pic_remap() masks every IRQ line (0xFF) including IRQ2, the cascade
input for the slave PIC, and nothing ever unmasks it. Any IRQ in the
8-15 range (RTC, PS/2 mouse, ATA, ...) could therefore never be
delivered, even after calling pic_unmask_irq() for it. Unmask the
cascade line on the master whenever a slave IRQ is enabled.
---
 src/cpu/pic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/cpu/pic.c b/src/cpu/pic.c
index dcb3b8d..73b6444 100644
--- a/src/cpu/pic.c
+++ b/src/cpu/pic.c
@@ -44,6 +44,9 @@ void pic_unmask_irq(uint8_t irqline)
     if (irqline < 8) {
         port = PIC1_DATA;
     } else {
+        // IRQs 8-15 come in through the slave PIC, wired to the master's
+        // IRQ2 line: the cascade must be unmasked too or they never fire
+        outb(PIC1_DATA, inb(PIC1_DATA) & ~(1 << 2));
         port = PIC2_DATA;
         irqline -= 8;
     }