Re: [PATCH v1 2/2] gpio: ds4520: Add ADI DS4520 Regulator Support

[Michael Walle]

Am 2023-04-09 16:25, schrieb Sahin, Okan:
> > Fri, Apr 07, 2023 at 03:48:25PM +0200, Linus Walleij kirjoitti:
> > > On Wed, Apr 5, 2023 at 3:57 PM Michael Walle <michael@xxxxxxxx> 
> > > wrote:
> > >
> > > > OTOH I'm not sure the driver is doing it correctly, because it also
> > > > seems to switch the pullup resisters together with the direction.
> > > > I'm not sure that is correct. So there might be just one register
> > > > involved after all and the GPIO_REGMAP should work again.
> > >
> > > I'm pretty sure that should be in the .set_config() callback.
> > >
> > > > Also, according to the datasheet this has some nv memory (to set the
> > > > initial state of the GPIOs [?]). So it should really be a
> > > > multi-function device. I'm not sure if this has to be considered
> > > > right from the beginning or if the device support can start with
> > > > GPIO only and later be transitioned to a full featured MFD (probably with nvmem
> > support).
> > > That's a bit of a soft definition.
> > >
> > > If the chip is *only* doing GPIO and nvram it can be a GPIO-only
> > > device I think.
> > >
> > > The precedent is a ton of ethernet drivers with nvram for storing 
> > > e.g.
> > > the MAC address. We don't make all of those into MFDs, as the nvram 
> > > is
> > > closely tied to the one and only function of the block.
> >
> > I agree with Linus. This should be part of the actual (main) driver 
> > for the chip as many
> > do (like USB to serial adapters that have GPIO capability).

You mean the gpio driver is calling nvmem_register()? Yeah I agree, that
should work.

> I think gpio_regmap is not suitable for this driver as Michael stated.
> https://www.analog.com/media/en/technical-documentation/data-sheets/ds4520.pdf
> Please check block diagram. There are two input registers that control
> gpio state
> so gpio_regmap does not look ok for this. Am I missing something?

You mean F8/F9? That will work as they are for different GPIOs. What
doesn't work with gpio-regmap is when you need to modify two different
registers for one GPIO. Have a look at gpio_regmap_get() and
gpio_regmap_set(). If the default gpio_regmap_simple_xlate() doesn't 
work
you can use your own .xlate() op.

> Also, at this point I am not planning to add nvmem support.

That is a pity, because that is the whole use case for this gpio 
expander,
no? "Programmable Replacement for Mechanical Jumpers and Switches"

-michael