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

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Date:	Fri, 30 Aug 2013 12:17:08 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Linus Walleij <linus.walleij@...aro.org>
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 Friday 30 August 2013 10:07:23 Linus Walleij wrote:
> On Fri, Aug 30, 2013 at 2:05 AM, Laurent Pinchart 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

That's the job of the boot loader, isn't it ? :-)

-- 
Regards,

Laurent Pinchart

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