[PATCH v5 15/16] hw/char/pl011: Drain TX FIFO when no backend connected

[Philippe Mathieu-Daudé]

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

Signed-off-by: Philippe Mathieu-Daudé <phi...@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 b8cde03f98..cfa3fd3da4 100644
--- a/hw/char/pl011.c
+++ b/hw/char/pl011.c
@@ -229,6 +229,13 @@ 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(void *do_not_use, GIOCondition cond, void *opaque)
 {
     PL011State *s = opaque;
@@ -242,6 +249,12 @@ static gboolean pl011_xmit(void *do_not_use, GIOCondition 
cond, void *opaque)
         qemu_log_mask(LOG_GUEST_ERROR, "PL011 data written to disabled TX 
UART\n");
     }
 
+    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;
+    }
+
     data = fifo8_pop(&s->xmit_fifo);
     bytes_consumed = 1;
 
diff --git a/hw/char/trace-events b/hw/char/trace-events
index 4a9c0bd271..bf586ba664 100644
--- a/hw/char/trace-events
+++ b/hw/char/trace-events
@@ -63,6 +63,7 @@ pl011_fifo_rx_full(void) "RX FIFO now full, RXFF set"
 pl011_fifo_tx_put(uint8_t byte) "TX FIFO push char [0x%02x]"
 pl011_fifo_tx_xmit(int count) "TX FIFO pop %d 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 ")"
 
 # cmsdk-apb-uart.c
-- 
2.41.0