Re: [PATCH] gpio: omap-gpio: add support for pm_runtime autosuspend

[Tim Niemeyer <tim.niemeyer@corscience.de>]

Hello

Am Freitag, den 26.10.2012, 23:01 +0300 schrieb Felipe Balbi:
> Hi,
> 
> On Fri, Oct 26, 2012 at 03:19:13PM +0200, Tim Niemeyer wrote:
> > Adds support for configuring the omap-gpio driver use autosuspend for
> > runtime power management. This can reduce the latency in using it by
> > not suspending the device immediately on idle. If another access takes
> > place before the autosuspend timeout (2 secs), the call to resume the
> > device can return immediately saving some save/ restore cycles.
> > 
> > This removes also the bank->mod_usage counter, because this is already
> > handled in pm_runtime.
> > 
> > I use a gpio to monitor a spi transfer which occurs every 250µs. The
> > suspend overhead is to high, so almost every second transfer is lost.
> > This patch fixes that.
> > 
> > Signed-off-by: Tim Niemeyer <tim.niemeyer@corscience.de>
> > ---
> >  drivers/gpio/gpio-omap.c |   81 ++++++++++++++++++++++++---------------------
> >  1 files changed, 43 insertions(+), 38 deletions(-)
> > 
> > diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
> > index 94cbc84..708d5a9 100644
> > --- a/drivers/gpio/gpio-omap.c
> > +++ b/drivers/gpio/gpio-omap.c
> > @@ -31,6 +31,7 @@
> >  #include <asm/mach/irq.h>
> >  
> >  #define OFF_MODE	1
> > +#define GPIO_AUTOSUSPEND_TIMEOUT                2000
> 
> something just hit me... If you keep timeout at 2000 ms and you hook
> this up to an IRQ line, it's very unlikely GPIO will ever sleep.
> 
> Why did you choose 2000 ms ? Arbitrary value ?
Got it from the spi driver (27b5284cfbe187732ebb184b03ea693f44837f9d).
I have no problem with reducing this. As i don't know how much
power-overhead the suspend needs, what do you think is a good value in
terms of power-saving?

-- 
Tim Niemeyer

Corscience GmbH & Co. KG
Henkestr. 91
D-91052 Erlangen
Germany

e-mail: tim.niemeyer@corscience.de
Internet: www.corscience.de

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