tty: serial: omap-serial: wakeup latency constraint is in microseconds, not milliseconds
authorPaul Walmsley <paul@pwsan.com>
Thu, 26 Jan 2012 02:50:56 +0000 (19:50 -0700)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 9 Feb 2012 18:48:36 +0000 (10:48 -0800)
commit197234520bd83aba2199add57a9d2678ee7f9781
tree8923cb1ed877f40141db03873e830df00df4840c
parentbe4b0281956c5cae4f63f31f11d07625a6988766
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>
drivers/tty/serial/omap-serial.c