[PATCH 12/15] serial: 8250: allow low-level drivers to override break control

[Crescent Hsieh]

Some UARTs require driver-specific handling for break signaling, which
cannot be expressed by the generic 8250 break implementation alone.

Add an optional uart_port break_ctl callback and route
serial8250_break_ctl() through it when provided. Rename the existing
8250 implementation to serial8250_do_break_ctl() and export it under the
SERIAL_8250_PCI namespace so low-level drivers can reuse the default
8250 behavior when appropriate.

Signed-off-by: Crescent Hsieh <crescentcy.hsieh@xxxxxxxx>
---
 drivers/tty/serial/8250/8250_core.c |  2 ++
 drivers/tty/serial/8250/8250_port.c | 11 ++++++++++-
 include/linux/serial_8250.h         |  1 +
 include/linux/serial_core.h         |  1 +
 4 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index bfa421ab3253..0a3355eb4bc3 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -796,6 +796,8 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
 		uart->port.startup = up->port.startup;
 	if (up->port.shutdown)
 		uart->port.shutdown = up->port.shutdown;
+	if (up->port.break_ctl)
+		uart->port.break_ctl = up->port.break_ctl;
 	if (up->port.pm)
 		uart->port.pm = up->port.pm;
 	if (up->port.handle_break)
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index a17fdb5d68d2..72ecc0112b8a 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1937,7 +1937,7 @@ static void serial8250_set_mctrl(struct uart_port *port, unsigned int mctrl)
 		serial8250_do_set_mctrl(port, mctrl);
 }
 
-static void serial8250_break_ctl(struct uart_port *port, int break_state)
+void serial8250_do_break_ctl(struct uart_port *port, int break_state)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
 
@@ -1950,6 +1950,15 @@ static void serial8250_break_ctl(struct uart_port *port, int break_state)
 		up->lcr &= ~UART_LCR_SBC;
 	serial_port_out(port, UART_LCR, up->lcr);
 }
+EXPORT_SYMBOL_NS_GPL(serial8250_do_break_ctl, "SERIAL_8250_PCI");
+
+static void serial8250_break_ctl(struct uart_port *port, int break_state)
+{
+	if (port->break_ctl)
+		port->break_ctl(port, break_state);
+	else
+		serial8250_do_break_ctl(port, break_state);
+}
 
 /* Returns true if @bits were set, false on timeout */
 static bool wait_for_lsr(struct uart_8250_port *up, int bits)
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index 01efdce0fda0..5ae00dede026 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -192,6 +192,7 @@ void serial8250_do_shutdown(struct uart_port *port);
 void serial8250_do_pm(struct uart_port *port, unsigned int state,
 		      unsigned int oldstate);
 void serial8250_do_set_mctrl(struct uart_port *port, unsigned int mctrl);
+void serial8250_do_break_ctl(struct uart_port *port, int break_state);
 void serial8250_do_set_divisor(struct uart_port *port, unsigned int baud,
 			       unsigned int quot);
 int fsl8250_handle_irq(struct uart_port *port);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 666430b47899..d9e5e3d02003 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -463,6 +463,7 @@ struct uart_port {
 	void			(*shutdown)(struct uart_port *port);
 	void			(*throttle)(struct uart_port *port);
 	void			(*unthrottle)(struct uart_port *port);
+	void			(*break_ctl)(struct uart_port *port, int break_state);
 	int			(*handle_irq)(struct uart_port *);
 	void			(*pm)(struct uart_port *, unsigned int state,
 				      unsigned int old);
-- 
2.43.0