On 10/22/2012 02:21 AM, Linus Walleij wrote: > On Fri, Oct 19, 2012 at 8:10 PM, Tony Lindgren <[email protected]> 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.
That API sounds like something system-wide, which seems like it would be rather presumptuous (CPU/SoC support code couldn't execute it, since that would presume a facet of all board designs that could change in the future). Even a driver shouldn't be assuming this; it can't know what boards it gets used in ahead of time. Instead, it seems like the map registration code could easily look at all states defined for a device, and determine if the set of pins/groups used by those states was identical, and switch between up-front or dynamic registration as needed by the specific map entries. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
