ARM: meson: serial: tx_empty fails to check for transmitter busy

The tx_empty() uart_op should only return empty if both the transmit fifo
and the transmit state-machine are both idle. Add a test for the hardware's
XMIT_BUSY flag.

Note, this is possibly related to an issue where the port is being shutdown
with paritally transmitted characters in it.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Reported-by: Edward Cragg <edward.cragg@codethink.co.uk>
Tested-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
index b87eb97e5e7a..54d1b9591b8d 100644
--- a/drivers/tty/serial/meson_uart.c
+++ b/drivers/tty/serial/meson_uart.c
@@ -57,6 +57,7 @@
 #define AML_UART_RX_EMPTY               BIT(20)
 #define AML_UART_TX_FULL                BIT(21)
 #define AML_UART_TX_EMPTY               BIT(22)
+#define AML_UART_XMIT_BUSY              BIT(25)
 #define AML_UART_ERR                    (AML_UART_PARITY_ERR | \
                                          AML_UART_FRAME_ERR  | \
                                          AML_UART_TX_FIFO_WERR)
@@ -100,7 +101,8 @@ static unsigned int meson_uart_tx_empty(struct uart_port *port)
         u32 val;
 
         val = readl(port->membase + AML_UART_STATUS);
-        return (val & AML_UART_TX_EMPTY) ? TIOCSER_TEMT : 0;
+        val &= (AML_UART_TX_EMPTY | AML_UART_XMIT_BUSY);
+        return (val == AML_UART_TX_EMPTY) ? TIOCSER_TEMT : 0;
 }
 
 static void meson_uart_stop_tx(struct uart_port *port)