Re: [PATCH 1/6] gpio: make the gpiochip a real device

[Johan Hovold <johan@kernel.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