Re: [PATCH v5 3/5] mfd: airoha: Add support for Airoha EN7581 MFD

[Lee Jones <lee@xxxxxxxxxx>]

On Wed, 09 Oct 2024, Lee Jones wrote:

> On Wed, 09 Oct 2024, Lorenzo Bianconi wrote:
> 
> > On Oct 02, Lee Jones wrote:
> > > On Tue, 01 Oct 2024, Lorenzo Bianconi wrote:
> > > 
> > > > From: Christian Marangi <ansuelsmth@xxxxxxxxx>
> > > > 
> > > > Support for Airoha EN7581 Multi Function Device that
> > > > expose PINCTRL functionality and PWM functionality.
> > > 
> > > The device is a jumble of pinctrl registers, some of which can oscillate.
> > > 
> > > This is *still* not an MFD.
> > > 
> > > If you wish to spread this functionality over 2 drivers, use syscon to
> > > obtain the registers and simple-mfd to automatically probe the drivers.
> > 
> > Hi Lee,
> > 
> > IIUC you are suggesting two possible approaches here:
> > 
> > 1- have a single driver implementing both pinctrl and pwm functionalities.
> >    This approach will not let us reuse the code for future devices that
> >    have just one of them in common, like pwm (but we can live with that).
> 
> If you can have one without the other, then they are separate devices.
> 
> > 2- use a device node like the one below (something similar to [0])
> > 
> > system-controller@1fbf0200 {
> > 	compatible = "syscon", "simple-mfd";
> > 	reg = <0x0 0x1fbf0200 0x0 0xc0>;
> > 
> > 	interrupt-parent = <&gic>;
> > 	interrupts = <GIC_SPI 26 IRQ_TYPE_LEVEL_HIGH>;
> > 
> > 	gpio-controller;
> > 	#gpio-cells = <2>;
> > 
> > 	interrupt-controller;
> > 	#interrupt-cells = <2>;
> > 
> > 	pio: pinctrl {
> > 		compatible = "airoha,en7581-pinctrl";
> > 
> > 		[ some pinctrl properties here ]
> > 	};
> > 
> > 	#pwm-cells = <3>;
> > 
> > 	pwm {
> > 		compatible = "airoha,en7581-pwm";
> > 	};
> > };
> > 
> > Please correct me if I am wrong, but using syscon/simple-mfd as compatible
> > string for the 'parent' device, will require to introduce the compatible strings
> > even for the child devices in order to probe them, correct? 
> > If so, as pointed out by Christian, this is something nacked by Rob/Krzysztof/Conor
> > (this is the main reason why we introduced a full mfd driver here).
> > 
> > @Rob, Krzysztof, Conor: am I right?
> 
> I don't see why separate functionality shouldn't have separate
> compatible strings, even if the registers are together.  Register layout
> and functionality separation are not related.

We've been happy to support both pinctrl and pwm devices before:

  git grep "\-pinctrl\|\-pwm" -- drivers/mfd
  git grep "\-pinctrl\|\-pwm" -- arch/*/boot/dts

  git grep "\-pinctrl" -- arch/*/boot/dts | wc -l
  602
  git grep "\-pwm" -- arch/*/boot/dts | wc -l
  856

What makes this particular device different to all of the others?

-- 
Lee Jones [李琼斯]