linux-kernel - Re: [PATCH] pinctrl: sink pinctrldev_list

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Message-ID: <CACRpkdZieCmFnHCGUkv8EqcAtb3DA7dSZpimSdB4P81tZPJRoQ@mail.gmail.com>
Date:	Fri, 24 May 2013 10:04:44 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>,
	ext Tony Lindgren <tony@...mide.com>,
	Haojian Zhuang <haojian.zhuang@...aro.org>
Cc:	Linus Walleij <linus.walleij@...ricsson.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Stephen Warren <swarren@...dia.com>,
	Anmar Oueja <anmar.oueja@...aro.org>
Subject: Re: [PATCH] pinctrl: sink pinctrldev_list_mutex

On Mon, May 20, 2013 at 10:40 PM, Stephen Warren <swarren@...dotorg.org> wrote:

> This seems fine on the surface, but I do have one question:
>
> I think the pinctrl lock serves a couple of purposes:
>
> 1) Basic protection for accesses to the pinctrldev_list itself.
>
> This patch seems just fine w.r.t. this point.
>
> 2) Preventing pinctrl drivers from being unregistered (and their modules
> unloaded) when some operation is being performed on/to them.

Prevention of module unloading of pin controllers has never
been working properly, as there is no way to release the
pinctrl handles taken by different drivers.

I think that is why most pin controller drivers are bool rather
than tristate.

Currently only pinctrl-single is tristate. Part of me want to
change that to bool, I think it only will work when using the
single with hogs (that will be properly free:ed when unloading
the driver).

Tony: is this really working with non-hogs?

If we really want to support loading/unloading of pin controllers
I think the mutex is the least of the problems, and we should
probably create a separate lock for handling that instead of
relying on the list lock in that case.

While it's probably possible to *unload* the driver properly
after some hacking like this, we get to the problem of
re-probing the driver and re-associating all pinctrl handles
(at that point floating in space with no driver back-end)
with the driver again.

I feel this needs to be driven by someone who actually
need to load/unload pinctrl modules.

Yours,
Linus Walleij
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