From 73f6ccd9e7e140223f797e600f282c0f4e012535 Mon Sep 17 00:00:00 2001
From: Marcelo Araujo <araujo@FreeBSD.org>
Date: Wed, 16 Jan 2019 03:46:27 +0000
Subject: [PATCH] Fix broken uart on Win2016 guest.

Obtained from:	Joyent (commit/2bf1a940afbd1382faff159e7c93c72779ca10f4)
MFC after:	3 weeks.
---
 usr.sbin/bhyve/uart_emul.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/usr.sbin/bhyve/uart_emul.c b/usr.sbin/bhyve/uart_emul.c
index 3c45ac7fc95..c9d136930eb 100644
--- a/usr.sbin/bhyve/uart_emul.c
+++ b/usr.sbin/bhyve/uart_emul.c
@@ -431,6 +431,13 @@ uart_write(struct uart_softc *sc, int offset, uint8_t value)
 		sc->thre_int_pending = true;
 		break;
 	case REG_IER:
+		/* Assert an interrupt if re-enabling the THRE intr, since we
+		 * always report THRE as active in the status register.
+		 */
+		if ((sc->ier & IER_ETXRDY) == 0 &&
+		    (value & IER_ETXRDY) != 0) {
+			sc->thre_int_pending = true;
+		}
 		/*
 		 * Apply mask so that bits 4-7 are 0
 		 * Also enables bits 0-3 only if they're 1