Commit 4f22afe3 authored Jan 19, 2012 by Simon Glass Committed by Samuel Pascua Feb 09, 2018

serial: Fix wakeup init logic to speed up startup



The synchronize_rcu() call resulting from making every serial driver
wake-up capable (commit b3b708fa) slows boot down on my Tegra2x system
(with CONFIG_PREEMPT disabled).

But this is avoidable since it is the device_set_wakeup_enable() and then
subsequence disable which causes the delay. We might as well just make
the device wakeup capable but not actually enable it for wakeup until
needed.

Effectively the current code does this:

	device_set_wakeup_capable(dev, 1);
	device_set_wakeup_enable(dev, 1);
	device_set_wakeup_enable(dev, 0);

We can just drop the last two lines.

Before this change my boot log says:
[    0.227062] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[    0.702928] serial8250.0: ttyS0 at MMIO 0x70006040 (irq = 69) is a Tegra

after:
[    0.227264] Serial: 8250/16550 driver, 4 ports, IRQ sharing disabled
[    0.227983] serial8250.0: ttyS0 at MMIO 0x70006040 (irq = 69) is a Tegra

for saving of 450ms.

Suggested-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Samuel Pascua <pascua.samuel.14@gmail.com>

parent 3dc8de62

drivers/tty/serial/serial_core.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -2409,11 +2409,11 @@ int uart_add_one_port(struct uart_driver drv, struct uart_port uport)
		*/
		tty_dev = tty_register_device(drv->tty_driver, uport->line, uport->dev);
		if (likely(!IS_ERR(tty_dev))) {
		device_init_wakeup(tty_dev, 1);
		device_set_wakeup_enable(tty_dev, 0);
		} else
		device_set_wakeup_capable(tty_dev, 1);
		} else {
		printk(KERN_ERR "Cannot register tty device on line %d\n",
		uport->line);
		}

		/*
		* Ensure UPF_DEAD is not set.