usb: gadget: serial: fix Tx stall after buffer overflow

Symptom: application opens /dev/ttyGS0 and starts sending (writing) to
it while either USB cable is not connected, or nobody listens on the
other side of the cable. If driver circular buffer overflows before
connection is established, no data will be written to the USB layer
until/unless /dev/ttyGS0 is closed and re-opened again by the
application (the latter besides having no means of being notified about
the event of establishing of the connection.)

Fix: on open and/or connect, kick Tx to flush circular buffer data to
USB layer.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Reviewed-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index f986e5c559748d43fb598753a44ffaf46e0a081c..8167d379e115ba5ae7874478f863d0b16c84f4a4 100644 (file)
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -561,8 +561,10 @@ static int gs_start_io(struct gs_port *port)
        port->n_read = 0;
        started = gs_start_rx(port);
 
-       /* unblock any pending writes into our circular buffer */
        if (started) {
+               gs_start_tx(port);
+               /* Unblock any pending writes into our circular buffer, in case
+                * we didn't in gs_start_tx() */
                tty_wakeup(port->port.tty);
        } else {
                gs_free_requests(ep, head, &port->read_allocated);