From 95388b9e0745ca0125012f050c53f651811b5189 Mon Sep 17 00:00:00 2001 From: Fam Zheng Date: Fri, 19 May 2017 00:35:19 +0200 Subject: [PATCH 14/18] serial: only resample THR interrupt on rising edge of IER.THRI RH-Author: Fam Zheng Message-id: <20170519003523.21163-15-famz@redhat.com> Patchwork-id: 75370 O-Subject: [RHEL-7.3.z qemu-kvm PATCH 14/18] serial: only resample THR interrupt on rising edge of IER.THRI Bugzilla: 1452332 RH-Acked-by: Paolo Bonzini RH-Acked-by: Laurent Vivier RH-Acked-by: Eduardo Habkost From: Paolo Bonzini There is disagreement on whether LSR.THRE should be resampled when IER.THRI goes from 1 to 1. Bochs only does it if IER.THRI goes from 0 to 1; PCE does it even if IER.THRI is unchanged. But the Windows driver seems to always go from 1 to 0 and back to 1, so do things in agreement with Bochs, because the handling of thr_ipending was reported in 2010 (https://lists.gnu.org/archive/html/qemu-devel/2010-03/msg01914.html) as breaking DR-DOS Plus. Reported-by: Roy Tam Signed-off-by: Paolo Bonzini (cherry picked from commit 1645b8eee558ffe2389a081bf61d08a864c36d2c) Signed-off-by: Fam Zheng Signed-off-by: Miroslav Rezanina --- hw/char/serial.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) diff --git a/hw/char/serial.c b/hw/char/serial.c index e0d29a8..9986adf 100644 --- a/hw/char/serial.c +++ b/hw/char/serial.c @@ -306,10 +306,12 @@ static void serial_ioport_write(void *opaque, hwaddr addr, uint64_t val, s->divider = (s->divider & 0x00ff) | (val << 8); serial_update_parameters(s); } else { + uint8_t changed = (s->ier ^ val) & 0x0f; s->ier = val & 0x0f; /* If the backend device is a real serial port, turn polling of the modem - status lines on physical port on or off depending on UART_IER_MSI state */ - if (s->poll_msl >= 0) { + * status lines on physical port on or off depending on UART_IER_MSI state. + */ + if ((changed & UART_IER_MSI) && s->poll_msl >= 0) { if (s->ier & UART_IER_MSI) { s->poll_msl = 1; serial_update_msl(s); @@ -324,18 +326,23 @@ static void serial_ioport_write(void *opaque, hwaddr addr, uint64_t val, * This is not in the datasheet, but Windows relies on it. It is * unclear if THRE has to be resampled every time THRI becomes * 1, or only on the rising edge. Bochs does the latter, and Windows - * always toggles IER to all zeroes and back to all ones. But for - * now leave it as it has always been in QEMU. + * always toggles IER to all zeroes and back to all ones, so do the + * same. * * If IER.THRI is zero, thr_ipending is not used. Set it to zero * so that the thr_ipending subsection is not migrated. */ - if ((s->ier & UART_IER_THRI) && (s->lsr & UART_LSR_THRE)) { - s->thr_ipending = 1; - } else { - s->thr_ipending = 0; + if (changed & UART_IER_THRI) { + if ((s->ier & UART_IER_THRI) && (s->lsr & UART_LSR_THRE)) { + s->thr_ipending = 1; + } else { + s->thr_ipending = 0; + } + } + + if (changed) { + serial_update_irq(s); } - serial_update_irq(s); } break; case 2: -- 1.8.3.1