linux-kernel - Re: [PATCH] regulator: core: GPIO #0 is a valid GPIO

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Date:	Mon, 1 Sep 2014 13:49:47 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Dmitry Eremin-Solenikov <dmitry_eremin@...tor.com>
Cc:	Dirk Behme <dirk.behme@...bosch.com>, linux-kernel@...r.kernel.org,
	Liam Girdwood <lgirdwood@...il.com>,
	Gokulkrishnan Nagarajan <Gokulkrishnan.Nagarajan@...bosch.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] regulator: core: GPIO #0 is a valid GPIO

On Mon, Sep 01, 2014 at 04:35:27PM +0400, Dmitry Eremin-Solenikov wrote:
> On 09/01/2014 04:06 PM, Mark Brown wrote:

> >Please consider my point about making users instantly buggy - it's not
> >practical to introduce a new field into existing platform data which
> >needs initialization.  Disallowing the use of 0 as a GPIO seems more
> >practical here (in that it's something the platform can control with
> >more reliable coordination).

> I think that this makes other users buggy - those, whose platforms use GPIO
> numbering starting from 0. IMX platform does. legacy platforms do.

It means that they can't use this feature for these specific GPIOs
unless someone writes some code to make it happen either by renumbering
or by adding generic code that provides a way to specify this, it
doesn't make anything worse than it is already.

> Consider NO_IRQ which is still defined to -1 on ARM platforms. If a device
> does not have a connected IRQ, it has to explicitly specify -1 instead of
> specifying logical default 0. Is it so? What is so different with GPIOs and
> regulators?

As I'm getting fed up of pointing out we can't make existing users buggy
- we couldn't do it when we added support for enable GPIOs and we can't
do it now.  Exactly the same problem would occur if adding platform data
to specify an interrupt where none was previously specified (which is
why there's a move away from NO_IRQ being -1).

Please, you need to care about other users.

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