From mboxrd@z Thu Jan  1 00:00:00 1970
From: govindraj.ti@gmail.com (Govindraj)
Date: Fri, 27 Jan 2012 12:49:51 +0530
Subject: [PATCH v2 3/3] tty: serial: omap-serial: wakeup latency
 constraint is in microseconds, not milliseconds
In-Reply-To: <20120126025052.31613.37828.stgit@dusk>
References: <20120126024903.31613.24730.stgit@dusk>
 <20120126025052.31613.37828.stgit@dusk>
Message-ID: <CAAL8m4xSHTaSFjvHoFcxg3w8cm3M8qibRrhf+NMV2MZVNCt0Nw@mail.gmail.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Jan 26, 2012 at 8:20 AM, Paul Walmsley <paul@pwsan.com> wrote:
> 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: Kevin Hilman <khilman@ti.com>
> Cc: Govindraj.R <govindraj.raja@ti.com>
> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> Cc: Alan Cox <alan@linux.intel.com>
> Cc: Greg Kroah-Hartman <gregkh@suse.de>

Acked-by: Govindraj.R <govindraj.raja@ti.com>

> ---
> ?drivers/tty/serial/omap-serial.c | ? ?3 +--
> ?1 files changed, 1 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index 11fa156..72fa783 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -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);
>
>
>
> --
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