Re: [PATCH v2 10/16] gpio: add a reusable generic gpio_chip using regmap

[Michael Walle]

Hi Mark, Hi Bartosz, Hi Linus,

Am 2020-04-14 20:41, schrieb Michael Walle:
> Am 2020-04-14 19:00, schrieb Bartosz Golaszewski:
> > wt., 14 kwi 2020 o 12:07 Michael Walle <michael@xxxxxxxx> napisaÅ(a):
> > > >>
> > > >> So the best from a user perspective I've could come up with was:
> > > >>
> > > >>    ->base_reg = GPIO_REGMAP_ADDR(addr);
> > > >>
> > > >> I'm open for suggestions.
> > > >>
> > > >
> > > > Maybe setting the pointer to ERR_PTR(-ENOENT) which will result in
> > > > IS_ERR() returning true?
> > >
> > > Unfortunatly, its not a pointer, but only a regular unsigned int (ie
> > > the type the regmap API has for its "reg" property). It could be a
> > > pointer of course but then the user would have to allocate additional
> > > memory.
> > >
> > > -michael
> >
> > Eek, of course it's not a pointer. If possible I'd like to avoid this
> > GPIO_REGMAP_ADDR() macro, so how about having some separate field for
> > invalid offsets making every offset 'valid' by default?
>
> IMHO this has the same problems as mentioned in the response to Mark's
> idea. Normally, the user sets only some addresses, thus he has to mark
> all other as invalid. And if you add another address, you have to touch
> all the drivers to mark it as invalid.
>
> We could add some force bits like the "use_ack" flag in the bgpio 
> driver,
> where you can force the use of the value 0. But I'd really like to find
> a better way..

So what about the following:

#define GPIO_REGMAP_ADDR_ZERO (unsigned int)(-1)

So this way the user might assign the base addresses the normal way
except when he wants to use zero, in that case he has to use

  ->base_adr = GPIO_REGMAP_ADDR_ZERO;

gpio-regmap.c could use then:

if (base_addr)
  something_useful(gpio_regmap_addr(base_addr));

unsigned int gpio_regmap_addr(unsigned int addr)
{
  return (addr == GPIO_REGMAP_ADDR_ZERO) ? 0 : addr;
}

-michael