[PATCH v2] pinctrl: reserve pins when states are activated

Linus Walleij linus.walleij at linaro.org
Mon Oct 22 04:21:19 EDT 2012

On Fri, Oct 19, 2012 at 8:10 PM, Tony Lindgren <tony at atomide.com> wrote:
> [Me]
>> Instead: let use reserve the pins when the state is activated
>> and drop them when the state is disabled, i.e. when we move to
>> another state. This way different devices/functions can use the
>> same pins at different times.
> Hmm doesn't this mean that we are now doing lots of extra
> reserving and dropping of pins? Performance is important from
> latency point of view for cases where we need to remux pins
> constantly runtime PM.

It is only done in case the pinmux state is switched in runtime
suspend/resume, so it's e.g. possible to just alter the pin config.

But in general what you say is true.

We used to to the same thing by having drivers call
pinctrl_get()/pinctrl_put() in this case instead, but that went
away with the introduction of states, so we cannot encode
different pin sets with say
pinctrl_get(dev, "foo")/pinctrl_get(dev, "bar")
anymore since there is only one pinctrl handle per device,
but multiple states.

If this turns out to be a severe performance bottleneck, I
suggest to add some additional constraint API, like
pinctrl_set_pinmux_homegeneous_pinsets(true) that will
at runtime select whether the pin allocation is done when
getting the pinctrl handle instead.

Linus Walleij

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