linux-kernel - Re: [PATCH] RFC: pinctrl: grab default handler with bus notifiers

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Message-ID: <50A53304.6040904@wwwdotorg.org>
Date:	Thu, 15 Nov 2012 11:23:00 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Mark Brown <broonie@...nsource.wolfsonmicro.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>,
	Felipe Balbi <balbi@...com>, Benoit Cousson <b-cousson@...com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Mitch Bradley <wmb@...mworks.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Kevin Hilman <khilman@...com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Rickard Andersson <rickard.andersson@...ricsson.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH] RFC: pinctrl: grab default handler with bus notifiers

On 11/15/2012 07:03 AM, Linus Walleij wrote:
> On Tue, Nov 13, 2012 at 7:35 AM, Mark Brown
> <broonie@...nsource.wolfsonmicro.com> wrote:
>> On Mon, Nov 12, 2012 at 01:21:40PM -0700, Stephen Warren wrote:
>>> On 11/11/2012 05:22 AM, Linus Walleij wrote:
>>
>>>> Another solution that was discussed was whether to move
>>>> the default pinctrl handle and state grab to the device
>>>> core as an optional field in struct device itself, but
>>>> I'd like to first propose this less intrusive mechanism.
>>
>>> I think doing that approach makes a lot more sense; wouldn't it
>>> completely avoid the issues with deferred probe that this notifier-based
>>> method can't solve? It would also be very much in line with e.g.
>>> dev_get_regmap() - if every resource that a driver required were handled
>>> like that, then deferred probe could be significantly isolated into the
>>> driver core rather than in every driver...
>>
>> I have to say that I agree with this, notifiers seem to make life more
>> complicated for limited gain.  Otherwise I guess we could enhance
>> notifiers so that they're able to trigger deferrals?
> 
> OK I'll have to come up with a patch to the device core
> instead... it'll be much simpler anyway and if both of you guys
> can back it I guess Greg might be OK with it too.

I did have one thought here; how will this interact with hogs? If a
device's pinctrl configuration must be pinctrl_get()'d before the device
is probed, then a pinctrl device with hogs will never get probed because
it won't be registered to provide the pinctrl node parsing. Solutions
might include:

a) Some special case where if the pinctrl driver only can't probe due to
missing pinctrl from its own node, don't defer the probe, but defer the
pinctrl_get().

b) Separate out DT node parsing from device instantiation, so that the
driver can always parse the DT, without needing the context of a
specific pinctrl device to do so.

I haven't thought through this in any detail though.
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