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

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Message-ID: <CACRpkdYYp+2ZVUd+wxYwDdBC+Bxiv2_N-1JRrbXSjV3WxuF8+g@mail.gmail.com>
Date:	Tue, 23 Oct 2012 10:58:03 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Tony Lindgren <tony@...mide.com>
Cc:	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 9:07 PM, Tony Lindgren <tony@...mide.com> wrote:
> * Linus Walleij <linus.walleij@...aro.org> [121022 01:22]:

>> 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.
>
> Or maybe you could release + reserve the pins only if the
> pins change?

Umm... not quite following but show me the code :-D

In the code as it stands currently we only detect
if a state changes and then it assumes the old state need
to be deactivated before activating a new one.

I think that in order to do that for a state A->B transition
we need to:

1. Get the pins for mux setting A
2. Get the pins for mux setting B
3. Loop over the pin array and compare
4. If all are the same, goto 7
5. Release pins for setting A
6. Acquire pins for setting B
7. Update all pin descs to point to setting B
8. Done

Hm, I can see a patch like that...

Yours,
Linus Walleij
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