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

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Message-ID: <CACRpkdYxvBvYAnmp-p5WwB3QD0rd83qDcdg-BMhN7-2Jv8Oo_w@mail.gmail.com>
Date:	Sat, 25 May 2013 11:09:54 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	ext Tony Lindgren <tony@...mide.com>,
	Haojian Zhuang <haojian.zhuang@...aro.org>,
	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 Fri, May 24, 2013 at 5:45 PM, Stephen Warren <swarren@...dotorg.org> wrote:
> On 05/24/2013 02:04 AM, Linus Walleij wrote:

>> 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.
>
> Once we get to multi-platform distro kernels, we will probably want all
> the pinctrl drivers to be modules so only the correct one gets loaded
> from an initrd. Hence, we'll want to move things to tristate rather than
> away from it.

OK ... As some kind of excuse I think the current situation is an
outgrowth of the fact that all the custom set-up used to be in machines
down in arch/arm/* and inevitably done at machine init.

> If we know the pinctrl subsystem doesn't yet work correctly with module
> unloads, should we modify pinctrl_register() to simply take a lock on
> the driver module and never drop it, so that we guarantee we don't try
> to unload the module later? Or, is this effectively already in place?

Hm, it won't happen with anything but pinctrl-single for sure.
But I know that Tony used it at one point, however I still
suspect that he was only using hogs.

We should maybe take the lock at the instant we instatiate a
pinctrl handle from something else than a hog, so as to mark
that we then have external dependencies that make unloading
impossible.

But it'd be even cooler to actually just iterate over the
pinctrl_list och handles and orphan them, and later recouple
them if a driver is loaded back in.

It can surely be done, but at the cost of introducing a state
lock in struct pinctrl and some pieces of hairy code in the
core.

Yours,
Linus Walleij
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