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

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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>
This commit is contained in:
Paul Walmsley 2012-01-25 19:50:56 -07:00 committed by Greg Kroah-Hartman
parent edbe5dbefe
commit 6bbcbf2208
1 changed files with 1 additions and 2 deletions
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3
drivers/tty/serial/omap-serial.c
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@ -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);