Enable buttons GPIO passthrough

[Andrew Jeffery]

Hi  Kwin,

On Fri, 8 Feb 2019, at 22:31, Linus Walleij wrote:
> > +static int aspeed_gpio_pass_through(struct gpio_chip *chip, unsigned int offset,
> > +                                   unsigned long usecs)
> > +{
> > +       printk("kwin::aspeed_gpio_pass_through is called");
> > +       return 0;
> > +}
> 
> I guess you want to actually implement this too :D

Something to keep in mind is that the ASPEED pinctrl already supports configuring the
passthrough bits. What we don't want is to cause some inconsistent state between
the GPIO and pinmux subsystems by just whacking the bits directly.

Looks like we should be able to make it work with PIN_MAP_MUX_GROUP() and using
some custom name for the state (maybe "passthrough")? It's a half-baked thought
though so I'm not sure if it's feasible let alone acceptable, but hopefully Linus can
comment.

Andrew