Re: gpio-omap: add support gpiolib bias (pull-up/down) flags?

[Drew Fustini <pdp7pdp7@gmail.com>]

On Thu, Mar 12, 2020 at 1:43 PM Linus Walleij <linus.walleij@linaro.org> wrote:
> Do we have a datasheet for this GPIO block somewhere? Should
> be the datasheet for the ASIC.

I am looking at the AM335x reference manual [0] but I can not actually
find any references to pull-up/down or bias for GPIO pins.  I guess I
was making of the mistake of assuming this would be something the gpio
pins support.

> We already have the required .set_config() callback on the OMAP
> driver, it's just that it only uses it for debounce.
>
> The driver is a bit convoluted with register offsets in a struct
> omap_gpio_reg_offs depending on variant, but if they have
> a register for this I'd say just get hacking.
>
> If the GPIO driver is using pin control as back-end you are
> looking at something more complex similar to what Intel is
> doing inside drivers/pinctrl/intel/pinctrl-intel.c: this driver
> is just calling up to gpiochip_generic_config() which will
> try to configure the lines behind the GPIO using pin config,
> which works if the proper ranges are defined so the
> framework can map a GPIO line to a pin control pin.

Thank you for the feedback, Linus.

Upon further review of drivers/pinctrl/pinctrl-single.c, I am not
certain it actually supports pull-up/down.

I see there is pcs_pinconf_clear_bias() and pcs_pinconf_bias_disable()
but I don't see a place where the PIN_CONFIG_BIAS_PULL_DOWN or
PIN_CONFIG_BIAS_PULL_UP get set.

I'll have to look at that some more before I go back to thinking about
how to integrate into gpio-omap.

Thanks,
Drew

[0] http://www.ti.com/lit/ug/spruh73q/spruh73q.pdf