linux-kernel - Re: [PATCH v4] gpio: pcf857x: Add OF support

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Date:	Fri, 30 Aug 2013 10:07:23 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	Alexandre Courbot <acourbot@...dia.com>
Subject: Re: [PATCH v4] gpio: pcf857x: Add OF support

On Fri, Aug 30, 2013 at 2:05 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> On Thursday 29 August 2013 14:16:59 Linus Walleij wrote:
>> On Mon, Aug 26, 2013 at 3:45 PM, Laurent Pinchart wrote:

>> Don't we want to do this generic if we shall do it?
>>
>> Like for *any* GPIO chips we provide lines-initial state in the device
>> tree and some code in the gpiochip with a callback in struct gpio_chip
>> that can be called by the gpiolib core to set this up? Then we don't
>> have to reimplement this for every GPIO controller that needs it.
>
> Most GPIO chips will provide a way to read back the current state. The initial
> state only needs to be provided for write-only chips. This is (luckily) rather
> an exception, so I don't think we should implement it in the core, at least
> not yet. We can always refactor the code later if needed, the proposed DT
> binding is generic enough.

But I think this can be useful on any GPIO chip.

For someone deploying some system and hacking around in the
device tree to set the GPIOs up properly at boot it can be a
real useful tool.

Or is that giving them too much rope? :-D

Yours,
Linus Walleij
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