Commit 19723452 authored Jan 25, 2012 by Paul Walmsley Committed by Greg Kroah-Hartman Feb 09, 2012

tty: serial: omap-serial: wakeup latency constraint is in microseconds, not milliseconds



The receive FIFO wakeup latency estimate in the omap-serial driver is
three orders of magnitude too small.  This effectively prevents the
MPU from going to a low-power state when CONFIG_CPU_IDLE=y.  This is a
major power management regression and masks some other FIFO-related
bugs in the driver.

Fix by correcting the most egregious problem in the RX wakeup latency
estimate.  There are several other flaws in the estimator; these will
be fixed by a separate patch series intended for 3.4.

The difference in low-power states with this patch can be observed via
debugfs in pm_debug/count.

This estimate does not have any effect when CONFIG_CPU_IDLE=n.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Alan Cox <alan@linux.intel.com>
Acked-by: Govindraj.R <govindraj.raja@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Tested-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent be4b0281

drivers/tty/serial/omap-serial.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -740,8 +740,7 @@ serial_omap_set_termios(struct uart_port port, struct ktermios termios,
		quot = serial_omap_get_divisor(port, baud);

		/* calculate wakeup latency constraint */
		up->calc_latency = (1000000 * up->port.fifosize) /
		(1000 * baud / 8);
		up->calc_latency = (USEC_PER_SEC * up->port.fifosize) / (baud / 8);
		up->latency = up->calc_latency;
		schedule_work(&up->qos_work);