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

Andy Shevchenko
2020-11-09T19:01:50Z

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:

...

> >> 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.

Yes. Both are correct. They are simply not applicable for everything
(it's not a silver bullet).

> I want my device to be configured with either DT or software_nodes
> created at run time with configfs.

Okay.

> My device is going to use GPIOs
> described in the DT and it is going to be configured via configfs at run
> time.

How is this related to swnodes?
Create GPIO lookup table.

> 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.

gpiod_add_lookup_table().

> >> At the moment the driver gets the list from fwnode/of_node. The list
> >> contain references to phandles which get resolved and and the driver
> >> ends up with a bunch of gpio descriptors. Great.
> >>
> >> This example looks nice but does the code that reads the reference from
> >> the gpios property and returns a gpiod actually exist? If it doesn't, I
> >> am willing to write it.
> >>
> >> At first glance it makes more sense to me to pass (struct gpiod_lookup
> >> *) instead of (struct software_node *) and make gpiolib's gpiod_find()
> >> accept lookup tables as parameter instead of searching the
> >> gpio_lookup_list? Or do you think such temporary table should be
> >> assembled from the above structure and then used in gpiod_find()?
> >>
> >> Any other suggestions on how to get a bunch of gpios (the description
> >> for gpios is available in the devicetree) for a device described with a
> >> software nodes?

--
With Best Regards,
Andy Shevchenko