From 56d1451e94896e42eca4e06ee2fb9c9fb2b36bb9 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Thu, 9 Dec 1999 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1999-12-09

---
 pc/devusb.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/pc/devusb.c b/pc/devusb.c
index d5c60d19f152de268231e3c1051d1400476c9acd..47ded81f75bc02eef628778bd56495b1f1d16987 100644
--- a/pc/devusb.c
+++ b/pc/devusb.c
@@ -1280,7 +1280,12 @@ usbreset(void)
 		delay(4);
 	}
 	outb(port+SOFMod, i);
-	// Interrupt handler
+	/*
+	 * Interrupt handler.
+	 * Bail out if no IRQ assigned by the BIOS.
+	 */
+	if(cfg->intl == 0xFF)
+		return;
 	intrenable(cfg->intl, interrupt, ub, cfg->tbdf, "usb");
 
 	ub->io = port;