From mboxrd@z Thu Jan  1 00:00:00 1970
From: Johan Hovold <johan@kernel.org>
Subject: Re: [PATCH 1/6] gpio: make the gpiochip a real device
Date: Thu, 5 Nov 2015 10:44:11 +0100
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To: Linus Walleij <linus.walleij@linaro.org>
Cc: Johan Hovold <johan@kernel.org>, "linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>, Alexandre Courbot <acourbot@nvidia.com>, Arnd Bergmann <arnd@arndb.de>, Michael Welling <mwelling@ieee.org>, Markus Pargmann <mpa@pengutronix.de>, Mark Brown <broonie@kernel.org>, Amit Kucheria <amit.kucheria@linaro.org>

On Wed, Nov 04, 2015 at 11:48:47AM +0100, Linus Walleij wrote:
> On Tue, Nov 3, 2015 at 10:24 PM, Linus Walleij <linus.walleij@linaro.org> wrote:
> > On Mon, Nov 2, 2015 at 11:31 AM, Johan Hovold <johan@kernel.org> wrote:
> >> On Thu, Oct 22, 2015 at 10:32:25AM +0200, Linus Walleij wrote:
> >
> >>> +      * We memset the struct to zero to avoid reentrance issues.
> >>> +      */
> >>> +     memset(&chip->device, 0, sizeof(chip->device));
> >>
> >> This is an indication of a larger problem.
> >>
> >> First of all, you must never register the same device structure twice.
> >>
> >> And the larger problem is: With the current interface where a struct
> >> gpio_chip is passed and registered, how would you prevent the device
> >> from going away while in use?
> >
> > OK I see. What about the design pattern elsewhere to pass a
> > gpiochip desc and have a new gpiochip_register() create the
> > gpiochip and delete gpiochip_add()?
> >
> > That's the usual pattern in subsystems.
> 
> Thinking about it maybe it's simplest to just make ->dev a pointer
> and kzalloc() it at gpiochip_add().
> 
> That should solve this.

You'd avoid ever reregistering the same struct device, but that would
not solve the bigger life-time issue by itself.

Johan