[PATCH 4.7 03/45] serial: 8250_port: fix runtime PM use in __do_stop_tx_rs485()

From: Greg Kroah-Hartman
Date: Fri Oct 21 2016 - 05:19:21 EST

4.7-stable review patch. If anyone has any objections, please let me know.


From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

commit b3965767d86cf4534dfe1affbde0453d3224ed7f upstream.

There are calls to serial8250_rpm_{get|put}() in __do_stop_tx_rs485() that are
certainly placed in a wrong location. I dunno how it had been tested with
runtime PM enabled because it is obvious "sleep in atomic context" error.

Besides that serial8250_rpm_get() is called immediately after an IO just
happened. It implies that the device is already powered on, see implementation
of serial8250_em485_rts_after_send() and serial8250_clear_fifos() for the

There is no bug have been seen due to, as I can guess, use of auto suspend mode
when scheduled transaction to suspend is invoked quite lately than it's needed
for a few writes to the port. It might be possible to trigger a warning if
stop_tx_timer fires when device is suspended.

Refactor the code to use runtime PM only in case of timer function.

Fixes: 0c66940d584d ("tty/serial/8250: fix RS485 half-duplex RX")
Cc: "Matwey V. Kornilov" <matwey@xxxxxxxxxx>
Tested-by: Yegor Yefremov <yegorslists@xxxxxxxxxxxxxx>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/tty/serial/8250/8250_port.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)

--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1415,12 +1415,8 @@ static void __do_stop_tx_rs485(struct ua
if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) {

- serial8250_rpm_get(p);
serial_port_out(&p->port, UART_IER, p->ier);
- serial8250_rpm_put(p);

@@ -1430,6 +1426,7 @@ static void serial8250_em485_handle_stop
struct uart_8250_em485 *em485 = p->em485;
unsigned long flags;

+ serial8250_rpm_get(p);
spin_lock_irqsave(&p->port.lock, flags);
if (em485 &&
em485->active_timer == &em485->stop_tx_timer) {
@@ -1437,6 +1434,7 @@ static void serial8250_em485_handle_stop
em485->active_timer = NULL;
spin_unlock_irqrestore(&p->port.lock, flags);
+ serial8250_rpm_put(p);

static void __stop_tx_rs485(struct uart_8250_port *p)
@@ -1476,7 +1474,7 @@ static inline void __stop_tx(struct uart
unsigned char lsr = serial_in(p, UART_LSR);
* To provide required timeing and allow FIFO transfer,
- * __stop_tx_rs485 must be called only when both FIFO and
+ * __stop_tx_rs485() must be called only when both FIFO and
* shift register are empty. It is for device driver to enable
* interrupt on TEMT.
@@ -1485,9 +1483,10 @@ static inline void __stop_tx(struct uart

em485->active_timer = NULL;
+ __stop_tx_rs485(p);
- __stop_tx_rs485(p);

static void serial8250_stop_tx(struct uart_port *port)