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>
diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 18d1324..f809041 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -740,8 +740,7 @@
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);