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

[Felipe Balbi <balbi@ti.com>]

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On Fri, Oct 26, 2012 at 12:42:35PM +0200, Tim Niemeyer wrote:
> Am Freitag, den 26.10.2012, 11:03 +0300 schrieb Felipe Balbi:
> > Hi,
> > 
> > On Fri, Oct 26, 2012 at 09:55:30AM +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.
> > > 
> > > 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 |   23 ++++++++++++++++++-----
> > >  1 files changed, 18 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
> > > index 94cbc84..92f48cb 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
> > >  
> > >  static LIST_HEAD(omap_gpio_list);
> > >  
> > > @@ -628,8 +629,10 @@ static void omap_gpio_free(struct gpio_chip *chip, unsigned offset)
> > >  	 * If this is the last gpio to be freed in the bank,
> > >  	 * disable the bank module.
> > >  	 */
> > > -	if (!bank->mod_usage)
> > > -		pm_runtime_put(bank->dev);
> > > +	if (!bank->mod_usage) {
> > 
> > while at that I would drop this bank->mod_usage nonsense and let
> > power core handle reference counting.
> I looked at it, but i'm unsure about the GPIO_MOD_CTRL_BIT. The
> bank->mod_usage counter prevents omap_gpio_free() to disable the hole
> bank while another gpio is still in use.

pm core's usage count will do the same thing. If you request 6 gpios,
you will have 6 pm_runtime_get(). If you free 5 of those, you will have
5 pm_runtime_put_autosuspend() which will only decrement the counter and
do nothing else.

-- 
balbi

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