On Sat, Jan 17, 2015 at 1:11 AM, Ray Jui [off-list ref] wrote:

On 1/16/2015 2:14 AM, Linus Walleij wrote:

quoted

Some hardware designs put the software-controlled biasing
resistors in the GPIO block electronically connected to the actual
pins, so that e.g. the biasing will be available if some MMC or
whatever is using the same pins in another muxing. In such
situations it's quite evident that they need to be a combined
GPIO and pin controller.

I have some regrets that bolting a second pin controller to the
GPIO chip make things a bit complex but it's a price we have
to pay for getting some kind of generic interface.

Okay. In summary, I think both of us think the following approach makes
sense in my situation:
- leave pinmux in pinctrl-bcm-cygnus.c
- leave pinctrl + gpio in pinctrl-bcm-cygnus-gpio.c under drivers/pinctrl/*

But by thinking about this more, I thought this would create duplicated
pinctrl descriptors in our system, one from the pinmux driver, and the
other from this pinctrl+gpio driver. That is probably undesirable?

No, there are several systems with multiple pin controllers and the
framework easily handles multiple pin controllers in the same
system just as well as we handle multiple GPIO chips.

By reviewing various drivers in the pinctrl directory, I found what
pinctrl-u300.c and pinctrl-coh901.c does seems to serve as a good model
for me to follow:
- pinctrl-u300.c is the pinmux driver
- pinctrl-coh901.c is the gpio+pinctrl driver

Yeah, I don't know if the separation between them is as beautiful
as it should be. I used it when developing the pin control
subsystem.

The GPIO pinctrl logic is in the coh901 block, so pinctrl-coh901.c
exposed two public functions u300_gpio_config_get, u300_gpio_config_set
that pinctrl-u300.c can use. The u300 populates all pinmux/pinctrl
related functions into the subsystem. This way there's only one pinctrl
descriptor, populated through pinctrl-u300.c.

Does that model make more sense to you?

Yeah I wrote it myself so I'm maybe blind for any dumbness in
the code. But I think it's kind of elegant. But it is not using the
generic pinctrl device tree bindings so it's kind of oldstyle and
bloated in that sense.

Yours,
Linus Walleij