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

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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>
This commit is contained in:
Russell King 2008-02-04 22:27:52 -08:00 committed by Linus Torvalds
parent 9d778a6937
commit c8c6bfa39d
1 changed files with 7 additions and 1 deletions
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8
drivers/serial/serial_core.c
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@ -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);
}