Re: [PATCH 0/3] Renesas RZ PFC and GPIO driver

[Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>]

Hi Chris,

On Monday 09 Jan 2017 21:08:49 Chris Brandt wrote:
> On Monday, January 09, 2017, Laurent Pinchart wrote:
> > Pin control on the Renesas RZ chips is performed per pin instead of per
> > function (but unfortunately with the various bits of configuration split
> > across a bunch of registers, otherwise we could have used pinctrl-single).
> 
> I will say this...'spoilier alert'...you're not going to see this particular
> PFC HW much anymore in the RZA series.
> 
> It will still be a 'per pin control' like the existing RZ/A1, but the bits
> will not be spread out over a bunch of registers. So something like
> pinctrl-single should work.

Both the existing RZ/A model and the pinctrl model are in my opinion 
improvements over the RZ/G and R-Car models. I don't care much about whether 
pinctrl-single can be used, but we really need hardware architectures that 
don't require those huge data tables.

> No idea about the future of RZG series.

I'll cross my fingers.

> > This gives us an opportunity to move away from the sh-pfc awful (but more
> > or less needed for the R-Car family) architecture and implement something
> > much, much cleaner without all those obscure data tables and macros, with
> > per-pin configuration. Shouldn't we rejoice and embrace that opportunity ?
> 
> Honestly, that driver structure confuses the heck out of me. I guess you
> have to understand the restrictions of the R-Car PFC HW to really
> appreciate it.

No, you can't appreciate it, no matter what :-)

> Of course I like the idea of a simple PFC for Renesas SoCs, of course the
> existing RZ/A1 would be (hopefully) the worst case scenario.
> 
> I assume to make a one-size-fits-all per-pin driver, instead of filling out
> structures and enums, you'd have to have callback functions that basically
> you pass "set pin X to function #3"...which basically brings you back to
> what the core of the pinctrl system does now any (if I understand it
> correctly).

It's more complex than that. Both the pin-based and group-based models have 
their pros and cons, and the pinctrl API is some kind of mix that allows both 
options.

-- 
Regards,

Laurent Pinchart

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