Re: [PATCH 1/2] dt-bindings: pinctrl: airoha: Add EN7581 pinctrl controller

[Lorenzo Bianconi <lorenzo@kernel.org>]

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On Aug 18, Andrew Lunn wrote:
> On Sun, Aug 18, 2024 at 02:48:05PM +0200, Benjamin Larsson wrote:
> > On 17/08/2024 23:39, Andrew Lunn wrote:
> > > How messy are the GPIO and PWM registers? Are there N blocks of
> > > independent GPIO registers? and M blocks of independent PWM registers?
> > > By that, does one block of GPIO registers contain all you need for one
> > > GPIO controller? One block of PWM registers give you all you need for
> > > one PWM controller? Or are the registers for one GPIO controller
> > > scattered all over the place?
> > > 
> > > Could you point at a public datasheet?
> > > 
> > >        Andrew
> > > 
> > Hi, per my understanding there is no public datasheet/register reference
> > manual.
> > 
> > But here is the division of regions of the registers in the gpio block and
> > how it is currently divided between the drivers (according to my current
> > understanding).
> > 
> > 1FBF0200, gpio/pinctrl
> > 1FBF0204, gpio/pinctrl
> > 1FBF0208, gpio/pinctrl
> > 1FBF020C, gpio/pinctrl
> > 1FBF0210, gpio/pinctrl
> > 1FBF0214, gpio/pinctrl
> 
> A typical SoC has multiple instances of a GPIO controller. Each GPIO
> controller typically has 4 or 5 registers: In, Out, Direction,
> Interrupt Enable, Interrupt Status. If these 4 or 5 registers are
> contiguous, you could have one DT node per controller, rather than one
> node for all GPIO controllers.

it is the same for en7581 pinctrl too. I think we can squash most of the
gpio/irq registers into "bigger" io-regions (just keeping a couple of holes
for pwm and leds). It is just a matter of moving the logic from the dts to
the driver. I am currently working on it. I will post v2 soon.

> 
> If the hardware designer has really messed up and fully interleaved
> GPIO and PWM, it might be better to have an MFD. The MFD node has a
> single reg covering the entire range. The MFD would then map the whole
> range, and provide accessors to the child devices. Hard code the
> knowledge of what registers are where. Given how badly the hardware is
> designed, it is unlikely it will get reused in the future, so there is
> no point putting lots of stuff into DT. Hard code it.

I am not sure it is possible/feasible to implement a MFD device here since
the mapped region is huge and sparse.

Regards,
Lorenzo

> 
> 	Andrew

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