From: Russell King Some ports seem to be unable to drain their transmitters on shut down. Such a problem can occur if the port is programmed for hardware imposed flow control, characters are in the FIFO but the CTS signal is inactive. Normally, this isn't a problem because most places where we wait for the transmitter to drain have a time-out. However, there is no timeout in the suspend path. Give a port 30ms to drain; this is an arbitary value chosen to avoid long delays if there are many such ports in the system, while giving a reasonable chance for a single port to drain. Should a port not drain within this timeout, issue a warning. Signed-off-by: Russell King Cc: Alan Cox Signed-off-by: Andrew Morton --- drivers/serial/serial_core.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff -puN drivers/serial/serial_core.c~serial-avoid-stalling-suspend-if-serial-port-wont-drain drivers/serial/serial_core.c --- a/drivers/serial/serial_core.c~serial-avoid-stalling-suspend-if-serial-port-wont-drain +++ a/drivers/serial/serial_core.c @@ -1977,6 +1977,7 @@ int uart_suspend_port(struct uart_driver if (state->info && state->info->flags & UIF_INITIALIZED) { const struct uart_ops *ops = port->ops; + int tries; state->info->flags = (state->info->flags & ~UIF_INITIALIZED) | UIF_SUSPENDED; @@ -1990,9 +1991,14 @@ int uart_suspend_port(struct uart_driver /* * Wait for the transmitter to empty. */ - while (!ops->tx_empty(port)) { + for (tries = 3; !ops->tx_empty(port) && tries; tries--) { msleep(10); } + if (!tries) + printk(KERN_ERR "%s%s%s%d: Unable to drain transmitter\n", + port->dev ? port->dev->bus_id : "", + port->dev ? ": " : "", + drv->dev_name, port->line); ops->shutdown(port); } _