[PATCH v2 3/6] serial: Implement flush callback

["Pali Rohár" <pali@kernel.org>]

UART drivers have putc/puts functions which just put characters into HW
transmit queue and do not wait until all data are transmitted.

Implement flush callback via serial driver's pending(false) callback which
waits until HW transmit all characters from the queue.

Signed-off-by: Pali Rohár <pali@kernel.org>
---
 drivers/serial/serial-uclass.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/serial/serial-uclass.c b/drivers/serial/serial-uclass.c
index 4b7819fa473b..71ea88e31c9f 100644
--- a/drivers/serial/serial-uclass.c
+++ b/drivers/serial/serial-uclass.c
@@ -238,6 +238,18 @@ static void _serial_puts(struct udevice *dev, const char *str)
 	} while (*str);
 }
 
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+static void _serial_flush(struct udevice *dev)
+{
+	struct dm_serial_ops *ops = serial_get_ops(dev);
+
+	if (!ops->pending)
+		return;
+	while (ops->pending(dev, false) > 0)
+		;
+}
+#endif
+
 static int __serial_getc(struct udevice *dev)
 {
 	struct dm_serial_ops *ops = serial_get_ops(dev);
@@ -412,6 +424,13 @@ static void serial_stub_puts(struct stdio_dev *sdev, const char *str)
 	_serial_puts(sdev->priv, str);
 }
 
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+static void serial_stub_flush(struct stdio_dev *sdev)
+{
+	_serial_flush(sdev->priv);
+}
+#endif
+
 static int serial_stub_getc(struct stdio_dev *sdev)
 {
 	return _serial_getc(sdev->priv);
@@ -571,6 +590,9 @@ static int serial_post_probe(struct udevice *dev)
 	sdev.priv = dev;
 	sdev.putc = serial_stub_putc;
 	sdev.puts = serial_stub_puts;
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+	sdev.flush = serial_stub_flush;
+#endif
 	sdev.getc = serial_stub_getc;
 	sdev.tstc = serial_stub_tstc;
 
-- 
2.20.1