serial: core: Fix runtime PM handling for pending tx

Richard reported that a serial port may end up sometimes with tx data pending in the buffer for long periods of time.

Turns out we bail out early on any errors from pm_runtime_get(), including -EINPROGRESS. To fix the issue, we need to ignore -EINPROGRESS as we only care about the runtime PM usage count at this point. We check for an active runtime PM state later on for tx.

Fixes 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM")

Reported-by Richard Purdie <[email protected]>

Cc Bruce Ashfield <[email protected]>

Cc Mikko Rapeli <[email protected]>

Cc Paul Gortmaker <[email protected]>

Cc Randy MacLeod <[email protected]>

Signed-off-by Tony Lindgren <[email protected]>

---
 drivers/tty/serial/serial_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

drivers/tty/serial/serial_core.c +1 -1

@@ -146,7 +146,7 @@ static void __uart_start(struct uart_state *state)
 
 	/* Increment the runtime PM usage count for the active check below */
 	err = pm_runtime_get(&port_dev->dev);
-	if (err < 0) {
+	if (err < 0 && err != -EINPROGRESS) {
 		pm_runtime_put_noidle(&port_dev->dev);
 		return;
 	}