Extract pl011_xmit() from pl011_write_txdata().
Use the FIFO to pass the single character to be transmitted.
Update flags appropriately.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/char/pl011.c      | 43 ++++++++++++++++++++++++++++++++++++-------
 hw/char/trace-events |  3 +++
 2 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/hw/char/pl011.c b/hw/char/pl011.c
index 0e9ad5d5d90..113b29cd9e6 100644
--- a/hw/char/pl011.c
+++ b/hw/char/pl011.c
@@ -226,6 +226,36 @@ static void pl011_loopback_tx(PL011State *s, uint32_t value)
     pl011_fifo_rx_put(s, value);
 }
 
+static void pl011_xmit(PL011State *s)
+{
+    int bytes_consumed;
+    uint8_t buf[PL011_FIFO_DEPTH];
+    uint32_t count;
+    bool emptied_fifo;
+
+    count = fifo8_num_used(&s->xmit_fifo);
+    trace_pl011_fifo_tx_xmit_used(count);
+
+    buf[0] = fifo8_pop(&s->xmit_fifo);
+    bytes_consumed = 1;
+
+    /*
+     * XXX this blocks entire thread. Rewrite to use
+     * qemu_chr_fe_write and background I/O callbacks
+     */
+    qemu_chr_fe_write_all(&s->chr, buf, bytes_consumed);
+    trace_pl011_fifo_tx_xmit_consumed(bytes_consumed);
+    s->int_level |= INT_TX;
+    s->flags &= ~PL011_FLAG_TXFF;
+
+    emptied_fifo = fifo8_is_empty(&s->xmit_fifo);
+    if (emptied_fifo) {
+        s->flags |= PL011_FLAG_TXFE;
+    }
+
+    pl011_update(s);
+}
+
 static void pl011_write_txdata(PL011State *s, uint8_t data)
 {
     if (!(s->cr & CR_UARTEN)) {
@@ -237,14 +267,13 @@ static void pl011_write_txdata(PL011State *s, uint8_t data)
                       "PL011 data written to disabled TX UART\n");
     }
 
-    /*
-     * XXX this blocks entire thread. Rewrite to use
-     * qemu_chr_fe_write and background I/O callbacks
-     */
-    qemu_chr_fe_write_all(&s->chr, &data, 1);
+    trace_pl011_fifo_tx_put(data);
     pl011_loopback_tx(s, data);
-    s->int_level |= INT_TX;
-    pl011_update(s);
+    fifo8_push(&s->xmit_fifo, data);
+    s->flags |= PL011_FLAG_TXFF;
+    s->flags &= ~PL011_FLAG_TXFE;
+
+    pl011_xmit(s);
 }
 
 static uint32_t pl011_read_rxdata(PL011State *s)
diff --git a/hw/char/trace-events b/hw/char/trace-events
index 05a33036c12..1bab98fb5f3 100644
--- a/hw/char/trace-events
+++ b/hw/char/trace-events
@@ -65,6 +65,9 @@ pl011_write(uint32_t addr, uint32_t value, const char *regname) "addr 0x%03x val
 pl011_can_receive(uint32_t lcr, unsigned rx_fifo_used, size_t rx_fifo_depth, unsigned rx_fifo_available) "LCR 0x%02x, RX FIFO used %u/%zu, can_receive %u chars"
 pl011_fifo_rx_put(uint32_t c, unsigned read_count, size_t rx_fifo_depth) "RX FIFO push char [0x%02x] %d/%zu depth used"
 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_used(unsigned sent) "TX FIFO used %u chars"
+pl011_fifo_tx_xmit_consumed(unsigned sent) "TX FIFO consumed %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