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

From: Linus Walleij
Date: Tue Oct 23 2012 - 05:31:06 EST

On Mon, Oct 22, 2012 at 10:30 PM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
> On 10/22/2012 02:21 AM, Linus Walleij wrote:

>> 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.

Well, yeah. It should rather be part of the pinctrl descriptor
then, so it becomes a per-controller runpath simplification.

> 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.

That kind of constraint-resolution in the kernel scares me,
soon we will have a prolog runtime ... (but hm maybe that is not
such a bad idea considering some other constraint things I've
seen around)

Linus Walleij
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