Re: [PATCH v1 1/2] dt-bindings: gpio: fairchild,74hc595: add registers-default property

Bartosz Golaszewski
2026-05-05T11:01:09Z

On Tue, May 5, 2026 at 11:46 AM Linus Walleij <linusw@kernel.org> wrote:
>
> On Wed, Apr 29, 2026 at 11:04 AM Bartosz Golaszewski <brgl@kernel.org> wrote:
>
> > > lines-initial-states:
> > > $ref: /schemas/types.yaml#/definitions/uint32
> > > description:
> > > Bitmask that specifies the initial state of each line.
> > > When a bit is set to zero, the corresponding line will be initialized to
> > > the input (pulled-up) state.
> > > When the bit is set to one, the line will be initialized to the
> > > low-level output state.
> > > If the property is not specified all lines will be initialized to the
> > > input state.
> > >
> > > If you want to set up initial states, use this property.
> > >
> > > This also makes it possible for us to centralize the handling later on.
> > >
> >
> > Ah, the old initial/default GPIO values problem strikes again. :(
> >
> > IMO this is software configuration, not HW description. I think the
> > driver should do it based on the compatible and/or machine. It should
> > not be a property but if Krzysztof is fine with it, I'll queue it.
>
> This one is particularly uncomfortably hard to define.
>
> If we depend on the machine we need to sprinkle
> of_machine_is_compatible() over all drivers.
>
> A lot of detailed properties that could have been handled by a few
> gazillion of_machine_is_compatible():s are already present
> in the kernel.
>
> What is good about the property that has the same name
> is that we can create nicer looking kernel code that is easier
> to maintain. The DT maintainers may not care about that, but
> from a GPIO subsystem PoV I think the line-initial-states
> are better.
>

Fair enough. I'll still wait for DT maintainers' formal Ack before we
carve it in stone do avoid getting hit on th ehead with said stone
later on. :)

Bart