new file mode 100644
@@ -0,0 +1,54 @@
+From 39da0e7957fb68b91f6c55cc61d66ae0930f3cd3 Mon Sep 17 00:00:00 2001
+From: Daniel Golle <daniel@makrotopia.org>
+Date: Thu, 6 Feb 2020 19:45:34 +0200
+Subject: [PATCH] serial: ar933x_uart: set UART_CS_{RX,TX}_READY_ORIDE
+To: linux-serial@vger.kernel.org,
+ linux-kernel@vger.kernel.org
+Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
+ Jiri Slaby <jslaby@suse.com>
+
+On AR934x this UART is usually not initialized by the bootloader
+as it is only used as a secondary serial port while the primary
+UART is a newly introduced NS16550-compatible.
+In order to make use of the ar933x-uart on AR934x without RTS/CTS
+hardware flow control, one needs to set the
+UART_CS_{RX,TX}_READY_ORIDE bits as other than on AR933x where this
+UART is used as primary/console, the bootloader on AR934x typically
+doesn't set those bits.
+Setting them explicitely on AR933x should not do any harm, so just
+set them unconditionally.
+
+Signed-off-by: Daniel Golle <daniel@makrotopia.org>
+---
+ drivers/tty/serial/ar933x_uart.c | 8 ++++++++
+ 1 file changed, 8 insertions(+)
+
+diff --git a/drivers/tty/serial/ar933x_uart.c b/drivers/tty/serial/ar933x_uart.c
+index 3bdd56a1021b..ea12f10610b6 100644
+--- a/drivers/tty/serial/ar933x_uart.c
++++ b/drivers/tty/serial/ar933x_uart.c
+@@ -286,6 +286,10 @@ static void ar933x_uart_set_termios(struct uart_port *port,
+ ar933x_uart_rmw_set(up, AR933X_UART_CS_REG,
+ AR933X_UART_CS_HOST_INT_EN);
+
++ /* enable RX and TX ready overide */
++ ar933x_uart_rmw_set(up, AR933X_UART_CS_REG,
++ AR933X_UART_CS_TX_READY_ORIDE | AR933X_UART_CS_RX_READY_ORIDE);
++
+ /* reenable the UART */
+ ar933x_uart_rmw(up, AR933X_UART_CS_REG,
+ AR933X_UART_CS_IF_MODE_M << AR933X_UART_CS_IF_MODE_S,
+@@ -418,6 +422,10 @@ static int ar933x_uart_startup(struct uart_port *port)
+ ar933x_uart_rmw_set(up, AR933X_UART_CS_REG,
+ AR933X_UART_CS_HOST_INT_EN);
+
++ /* enable RX and TX ready overide */
++ ar933x_uart_rmw_set(up, AR933X_UART_CS_REG,
++ AR933X_UART_CS_TX_READY_ORIDE | AR933X_UART_CS_RX_READY_ORIDE);
++
+ /* Enable RX interrupts */
+ up->ier = AR933X_UART_INT_RX_VALID;
+ ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
+--
+2.25.0
+
On AR934x this UART is usually not initialized by the bootloader as it is only used as a secondary serial port while the primary UART is a newly introduced NS16550-compatible. In order to make use of the ar933x-uart on AR934x without RTS/CTS hardware flow control, one needs to set the UART_CS_{RX,TX}_READY_ORIDE bits as other than on AR933x where this UART is used as primary/console, the bootloader on AR934x typically doesn't set those bits. Setting them explicitely on AR933x should not do any harm, so just set them unconditionally. Signed-off-by: Daniel Golle <daniel@makrotopia.org> --- If this works well on AR93xx there will be no need to add another compatible string and logic to differentiate between AR933x and AR934x in the UART driver. I don't have AR933x here to test, it'd be great if someone with that hardware can test if applying this patch breaks the serial console or not. ...uart-set-UART_CS_-RX-TX-_READY_ORIDE.patch | 54 +++++++++++++++++++ 1 file changed, 54 insertions(+) create mode 100644 target/linux/ath79/patches-4.19/0060-serial-ar933x_uart-set-UART_CS_-RX-TX-_READY_ORIDE.patch