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

[Michael Walle]

Hi Linus,

Am 2020-04-16 11:27, schrieb Linus Walleij:
> On Thu, Apr 2, 2020 at 10:37 PM Michael Walle <michael@xxxxxxxx> wrote:
>
> > There are quite a lot simple GPIO controller which are using regmap to
> > access the hardware. This driver tries to be a base to unify existing
> > code into one place. This won't cover everything but it should be a 
> > good
> > starting point.
> >
> > It does not implement its own irq_chip because there is already a
> > generic one for regmap based devices. Instead, the irq_chip will be
> > instanciated in the parent driver and its irq domain will be associate
> > to this driver.
> >
> > For now it consists of the usual registers, like set (and an optional
> > clear) data register, an input register and direction registers.
> > Out-of-the-box, it supports consecutive register mappings and mappings
> > where the registers have gaps between them with a linear mapping 
> > between
> > GPIO offset and bit position. For weirder mappings the user can 
> > register
> > its own .xlate().
> >
> > Signed-off-by: Michael Walle <michael@xxxxxxxx>
>
> Overall I really like this driver and I think we should merge is as 
> soon
> as it is in reasonable shape and then improve on top so we can start
> migrating drivers to it.
>
> > +static int gpio_regmap_to_irq(struct gpio_chip *chip, unsigned int 
> > offset)
> > +{
> > +       struct gpio_regmap_data *data = gpiochip_get_data(chip);
> > +       struct gpio_regmap *gpio = data->gpio;
> > +
> > +       /* the user might have its own .to_irq callback */
> > +       if (gpio->to_irq)
> > +               return gpio->to_irq(gpio, offset);
> > +
> > +       return irq_create_mapping(gpio->irq_domain, offset);
>
> I think that should at least be irq_find_mapping(), the mapping should
> definately not be created by the .to_irq() callback since that is just
> a convenience function.

what do you mean by conenience function? are there other ways? if you 
use
irq_find_mapping() who will create the mappings? most gpio drivers use a
similar function like gpio_regmap_to_irq().

> > +       if (gpio->irq_domain)
> > +               chip->to_irq = gpio_regmap_to_irq;
>
> I don't know about this.
> (...)
> > + * @irq_domain:                (Optional) IRQ domain if the 
> > controller is
> > + *                     interrupt-capable
> (...)
> > +       struct irq_domain *irq_domain;
>
> I don't think this is a good storage place for the irqdomain, we 
> already have
> gpio_irq_chip inside gpio_chip and that has an irqdomain, we should
> strive to reuse that infrastructure also for regmap GPIO I think, for 
> now
> I would just leave .to_irq() out of this and let the driver deal with 
> any
> irqs.

How would a driver attach the to_irq callback then? At the moment, the
gpio_regmap doesn't expose the gpio_chip. So either we have to do that 
or
the config still have to have a .to_irq property.

-michael