[Qemu-devel] [PATCH 2/3] serial: update LSR on enabling/disabling FIFOs

[Paolo Bonzini]

When the transmit FIFOs is enabled, it is emptied and thus the transmitter
hold register is empty.  When it is disabled, the previous contents
of the transmitter hold register are discarded.  In either case, the
THRE bit in LSR must be set and THRI raised.

When the receive FIFO is enable, it is emptied and thus the data ready
and break bits must be cleared in LSR.  Likewise when the receive FIFO
is disabled.

The transmit changes fix avoid the need for thr_ipending bandaids in the
routines that handle writes to IER.  Without this patch, the next patch
would cause a missed THRI interrupt and break the Windows COM driver.

Cc: address@hidden
Signed-off-by: Paolo Bonzini <address@hidden>
---
 hw/char/serial.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hw/char/serial.c b/hw/char/serial.c
index 4cd139f..f35fa42 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -363,12 +363,15 @@ static void serial_ioport_write(void *opaque, hwaddr 
addr, uint64_t val,
         /* FIFO clear */
 
         if (val & UART_FCR_RFR) {
+            s->lsr &= ~(UART_LSR_DR | UART_LSR_BI);
             timer_del(s->fifo_timeout_timer);
             s->timeout_ipending = 0;
             fifo8_reset(&s->recv_fifo);
         }
 
         if (val & UART_FCR_XFR) {
+            s->lsr |= UART_LSR_THRE;
+            s->thr_ipending = 1;
             fifo8_reset(&s->xmit_fifo);
         }
 
-- 
1.8.3.1