Re: [PATCH v8 3/6] software node: implement reference properties

Dmitry Torokhov
2020-11-09T18:53:12Z

On Mon, Nov 09, 2020 at 07:18:37PM +0100, Lukasz Stelmach wrote:
> It was <2020-11-09 pon 19:24>, when Andy Shevchenko wrote:
> > On Mon, Nov 09, 2020 at 06:02:29PM +0100, Lukasz Stelmach wrote:
> >> It was <2019-11-07 czw 20:22>, when Dmitry Torokhov wrote:
> >> > It is possible to store references to software nodes in the same fashion as
> >> > other static properties, so that users do not need to define separate
> >> > structures:
> >> >
> >> > static const struct software_node gpio_bank_b_node = {
> >> > .name = "B",
> >> > };
> >> >
> >> > static const struct property_entry simone_key_enter_props[] = {
> >> > PROPERTY_ENTRY_U32("linux,code", KEY_ENTER),
> >> > PROPERTY_ENTRY_STRING("label", "enter"),
> >> > PROPERTY_ENTRY_REF("gpios", &gpio_bank_b_node, 123, GPIO_ACTIVE_LOW),
> >> > { }
> >> > };
> >> >
> >> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
> >> > ---
> >>
> >> I am writing a piece that needs to provide a list of gpios to a
> >> diriver. The above example looks like what I need.
> >
> > Nope.
> >
> > It mustn't be used for GPIOs or PWMs or whatever that either should come via
> > lookup tables or corresponding firmware interface.
> >
>
> May I ask why? I've read commit descriptions for drivers/base/swnode.c
> and the discussion on lkml and I understand software nodes as a way to
> provide (synthesize) a description for a device that is missing a
> description in the firmware. Another use case seems to be to replace (in
> the long run) platform data. That is what I am trying to use it for.
>
> I want my device to be configured with either DT or software_nodes
> created at run time with configfs. My device is going to use GPIOs
> described in the DT and it is going to be configured via configfs at run
> time. I could use platform_data to pass structures from configfs but
> software nodes would let me save some code in the device driver and use
> the same paths for both static (DT) and dynamic (configfs)
> configuration.
>
> Probably I have missed something and I will be greatful, if you tell me
> where I can find more information about software nodes. There are few
> users in the kernel and it isn't obvious for me how to use software
> nodes properly.

Yeah, I disagree with Andy here. The lookup tables are a crutch that we
have until GPIO and PWM a taught to support software nodes (I need to
resurrect my patch series for GPIO, if you have time to test that would
be awesome).

Thanks.

--
Dmitry