When no character backend is connected, the PL011 frontend
just drains the FIFO.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/char/pl011.c      | 13 +++++++++++++
 hw/char/trace-events |  1 +
 2 files changed, 14 insertions(+)

diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index f67ce951ac9..6d26a3e13f8 100644
--- a/hw/char/pl011.c
+++ b/hw/char/pl011.c
@@ -241,6 +241,13 @@ static void pl011_loopback_tx(PL011State *s, uint32_t value)
     pl011_fifo_rx_put(s, value);
 }
 
+static void pl011_drain_tx(PL011State *s)
+{
+    trace_pl011_fifo_tx_drain(fifo8_num_used(&s->xmit_fifo));
+    pl011_reset_tx_fifo(s);
+    s->rsr &= ~RSR_OE;
+}
+
 static gboolean pl011_xmit_cb(void *do_not_use, GIOCondition cond, void *opaque)
 {
     PL011State *s = opaque;
@@ -252,6 +259,12 @@ static gboolean pl011_xmit_cb(void *do_not_use, GIOCondition cond, void *opaque)
     count = fifo8_num_used(&s->xmit_fifo);
     trace_pl011_fifo_tx_xmit_used(count);
 
+    if (!qemu_chr_fe_backend_connected(&s->chr)) {
+        /* Instant drain the fifo when there's no back-end. */
+        pl011_drain_tx(s);
+        return G_SOURCE_REMOVE;
+    }
+
     buf[0] = fifo8_pop(&s->xmit_fifo);
     bytes_consumed = 1;
 
diff --git a/hw/char/trace-events b/hw/char/trace-events
index d52f511a1e2..730d6292a2d 100644
--- a/hw/char/trace-events
+++ b/hw/char/trace-events
@@ -71,6 +71,7 @@ pl011_fifo_tx_put(uint8_t byte) "TX FIFO push char [0x%02x]"
 pl011_fifo_tx_xmit_used(unsigned sent) "TX FIFO used %u chars"
 pl011_fifo_tx_xmit_consumed(unsigned sent) "TX FIFO consumed %u chars"
 pl011_fifo_tx_overrun(void) "TX FIFO overrun"
+pl011_fifo_tx_drain(unsigned drained) "TX FIFO draining %u chars"
 pl011_baudrate_change(unsigned int baudrate, uint64_t clock, uint32_t ibrd, uint32_t fbrd) "new baudrate %u (clk: %" PRIu64 "hz, ibrd: %" PRIu32 ", fbrd: %" PRIu32 ")"
 pl011_receive(int size) "recv %d chars"
 
-- 
2.47.1