Commit c8c6bfa3 authored Feb 04, 2008 by Russell King Committed by Linus Torvalds Feb 05, 2008

serial: avoid stalling suspend if serial port won't drain



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 <rmk+kernel@arm.linux.org.uk>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 9d778a69

drivers/serial/serial_core.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -1977,6 +1977,7 @@ int uart_suspend_port(struct uart_driver drv, struct uart_port port)

		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 drv, struct uart_port port)
		/*
		* 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);
		}