Re: [Patch v2 1/2] gpio: add GPIO hogging mechanism

Benoit Parrot
2014-12-02T00:28:09Z

Maxime Ripard <maxime.ripard@free-electrons.com> wrote on Mon [2014-Dec-01 17:36:39 +0100]:
> Hi,
>
> On Fri, Nov 28, 2014 at 04:30:01PM +0900, Alexandre Courbot wrote:
> > > +/**
> > > + * do_gpio_hog - Given node is a GPIO hog configuration, handle it
> > > + * @np: device node to get GPIO from
> > > + *
> > > + * This is only used by of_gpiochip_add to request/set GPIO initial
> > > + * configuration.
> > > + */
> > > +static int do_gpio_hog(struct device_node *np)
> > > +{
> > > + struct gpio_desc *desc = NULL;
> > > + int err;
> > > + const char *name;
> > > + enum gpio_lookup_flags lflags;
> > > + enum gpiod_flags dflags;
> > > +
> > > + desc = of_get_gpio_hog(np, &name, &lflags, &dflags);
> > > + if (!desc)
> > > + return -ENOTSUPP;
> > > + else if (IS_ERR(desc))
> > > + return PTR_ERR(desc);
> > > +
> > > + err = gpiod_request(desc, name);
> >
> > Using this function means that a GPIO chip module cannot be unloaded
> > if it uses GPIO hogs. Is it the intended behavior? If not, please use
> > gpiochip_request_own_desc() instead, and make sure to call
> > gpiochip_free_own_desc() for each hog when the driver is unloaded.
>
> The only thing I'd like to have would be that the request here would
> be non-exclusive, so that a later driver would still be allowed later
> on to request that GPIO later on and manage it itself (ideally using
> the usual gpiod_request function).

I'll let Linus chime in on this.
But the premise for the hogging mechanism is to have a mechanism to set GPIOs
which do not need to be requested by any other entity.
If a driver needs access to a specific GPIO then it should use the existing
gpiolib API to request it and set it up.

>
> Maxime
>
> --
> Maxime Ripard, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com

Regards,
Benoit