Re: [PATCH 1/1] gpio: core: Decouple open drain/source flag with active low/high

[Laxman Dewangan]

On Thursday 06 April 2017 09:40 PM, Andy Shevchenko wrote:
> On Thu, Apr 6, 2017 at 4:35 PM, Laxman Dewangan <ldewangan@xxxxxxxxxx> wrote:
> > Currently, the GPIO interface is said to Open Drain if it is Single
> > Ended and active LOW. Similarly, it is said as Open Source if it is
> > Single Ended and active HIGH.
> >
> > The active HIGH/LOW is used in the interface for setting the pin
> > state to HIGH or LOW when enabling/disabling the interface.
> >
> > In Open Drain interface, pin is set to HIGH by putting pin in
> > high impedance and LOW by driving to the LOW.
> >
> > In Open Source interface, pin is set to HIGH by driving pin to
> > HIGH and set to LOW by putting pin in high impedance.
> >
> > With above, the Open Drain/Source is unrelated to the active LOW/HIGH
> > in interface. There is interface where the enable/disable of interface
> > is ether active LOW or HIGH but it is Open Drain type.
> >
> > Hence decouple the Open Drain with Single Ended + Active LOW and
> > Open Source with Single Ended + Active HIGH.
> >
> > Adding different flag for the Open Drain/Open Source which is valid
> > only when Single ended flag is enabled.
> >          if (single_ended) {
> > -               if (active_low)
> > +               if (open_drain)
> This breaks ACPI case, right?

In acpi case, single_ended is not handled. It only handles the active LOW.

From code:


       bool active_low = false;
        bool single_ended = false;
        int ret;

        if (!fwnode)
                return ERR_PTR(-EINVAL);

        if (is_of_node(fwnode)) {
                enum of_gpio_flags flags;

                desc = of_get_named_gpiod_flags(to_of_node(fwnode), 
propname,
                                                index, &flags);
                if (!IS_ERR(desc)) {
                        active_low = flags & OF_GPIO_ACTIVE_LOW;
                        single_ended = flags & OF_GPIO_SINGLE_ENDED;
                }
        } else if (is_acpi_node(fwnode)) {
                struct acpi_gpio_info info;

                desc = acpi_node_get_gpiod(fwnode, propname, index, &info);
                if (!IS_ERR(desc))
                        active_low = info.polarity == GPIO_ACTIVE_LOW;
        }