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

[Haojian Zhuang <haojian.zhuang@linaro.org>]

On Fri, 13 Mar 2020 at 08:38, Drew Fustini <pdp7pdp7@gmail.com> wrote:
>
> 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.
>

                        /* 4 parameters */
                        case PIN_CONFIG_BIAS_DISABLE:
                                pcs_pinconf_clear_bias(pctldev, pin);
                                break;
                        case PIN_CONFIG_BIAS_PULL_DOWN:
                        case PIN_CONFIG_BIAS_PULL_UP:
                                if (arg)
                                        pcs_pinconf_clear_bias(pctldev, pin);
                                /* fall through */
                        case PIN_CONFIG_INPUT_SCHMITT_ENABLE:
                                data &= ~func->conf[i].mask;
                                if (arg)
                                        data |= func->conf[i].enable;
                                else
                                        data |= func->conf[i].disable;
                                break;

Because it does fall through, pullup/pulldown is set in the snippet of
"PIN_CONFIG_INPUT_SCHMITT_ENABLE".

Best Regards
Haojian