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

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Message-ID: <CACRpkdY002gNuy81_XfenQfhZnMVyAxViMhoSd3nNMH5k0=JBQ@mail.gmail.com>
Date:	Tue, 23 Oct 2012 11:31:15 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Tony Lindgren <tony@...mide.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Stephen Warren <swarren@...dia.com>,
	Anmar Oueja <anmar.oueja@...aro.org>,
	Patrice Chotard <patrice.chotard@...com>,
	Jean Nicolas Graux <jean-nicolas.graux@...ricsson.com>,
	Loic Pallardy <loic.pallardy@...com>
Subject: Re: [PATCH v2] pinctrl: reserve pins when states are activated

On Mon, Oct 22, 2012 at 10:30 PM, Stephen Warren <swarren@...dotorg.org> 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)

Yours,
Linus Walleij
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