serial: apbuart: fix console prompt on qemu

[ Upstream commit c6dcd8050fb7c2efec6946ae9c49bc186b0a7475 ]

When using a leon kernel with qemu there where no console prompt.
The root cause is the handling of the fifo size in the tx part of the
apbuart driver.

The qemu uart driver only have a very rudimentary status handling and do
not report the number of chars queued in the tx fifo in the status register.
So the driver ends up with a fifo size of 1.

In the tx path the fifo size is divided by 2 - resulting in a fifo
size of zero.

The original implementation would always try to send one char, but
after the introduction of uart_port_tx_limited() the fifo size is
respected even for the first char.

There seems to be no good reason to divide the fifo size with two - so
remove this. It looks like something copied from the original amba driver.

With qemu we now have a minimum fifo size of one char, so we show
the prompt.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Fixes: d11cc8c3c4b6 ("tty: serial: use uart_port_tx_limited()")
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc:  <linux-serial@vger.kernel.org>
Cc:  <sparclinux@vger.kernel.org>
Link: https://lore.kernel.org/r/20231226121607.GA2622970@ravnborg.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/tty/serial/apbuart.c b/drivers/tty/serial/apbuart.c
index d7658f3..d3cb341 100644 (file)
--- a/drivers/tty/serial/apbuart.c
+++ b/drivers/tty/serial/apbuart.c
@@ -122,7 +122,7 @@ static void apbuart_tx_chars(struct uart_port *port)
 {
        u8 ch;
 
-       uart_port_tx_limited(port, ch, port->fifosize >> 1,
+       uart_port_tx_limited(port, ch, port->fifosize,
                true,
                UART_PUT_CHAR(port, ch),
                ({}));