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

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Message-ID: <CACRpkdaC54jJxfPiaEborfuozHCgvH6vMzsQT_6kJsM-=6fedQ@mail.gmail.com>
Date:	Wed, 29 May 2013 18:28:26 +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 Tue, May 28, 2013 at 5:14 PM, Stephen Warren <swarren@...dotorg.org> wrote:
> [Me]
>> 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.
>
> Hmm. What happens if the client driver wants to select a different state
> while the pinctrl driver itself isn't loaded? I'm not sure how workable
> that is. I think the only way to make it work would be to cache enough
> information in the struct pinctrl that it could be activated even if the
> driver wasn't loaded. That seems a little scary.

Yes it looks like that would lead to a bit of scalability problem in the
struct pinctrl. If for nothing else than for the fact that it will eat
memory and such :-(

> I'd be fine if there was a requirement to unload all drives that were
> clients of the pinctrl driver before you could unload the pinctrl
> driver, just like any other driver/subsystem. This would work fine at
> least for testing with just hogs, which while not great for full-system
> testing would surely be fine at least when first developing the pinctrl
> driver.

Yes ... so if we call
get_device(pctldev->dev)/put_device(pctldev->dev)
for any successful pinctrl_get() which is not a hog,
we increase the refcount so that the device core will disallow
unloading of the driver.

Now I need to figure out how to do that.

Yours,
Linus Walleij
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