Re: [net-next PATCH v2 10/14] device property: Introduce fwnode_get_id()

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Tue, Dec 15, 2020 at 7:00 PM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> On Tue, Dec 15, 2020 at 10:13:11PM +0530, Calvin Johnson wrote:
> > Using fwnode_get_id(), get the reg property value for DT node
> > and get the _ADR object value for ACPI node.

...

> > +/**
> > + * fwnode_get_id - Get the id of a fwnode.
> > + * @fwnode: firmware node
> > + * @id: id of the fwnode
>
> Is the concept of fwnode ID documented clearly somewhere ? I think this
> function should otherwise have more documentation, at least to explain
> what the ID is.

I'm afraid that OF has no clear concept of this either. It's usually
used as a unique ID for the children of some device (like MFD) and can
represent a lot of things. But I agree it should be documented.

Rob, any ideas about this?

> > + * Returns 0 on success or a negative errno.
> > + */
> > +int fwnode_get_id(struct fwnode_handle *fwnode, u32 *id)
> > +{
> > +     unsigned long long adr;
> > +     acpi_status status;
> > +
> > +     if (is_of_node(fwnode)) {
> > +             return of_property_read_u32(to_of_node(fwnode), "reg", id);
> > +     } else if (is_acpi_node(fwnode)) {
> > +             status = acpi_evaluate_integer(ACPI_HANDLE_FWNODE(fwnode),
> > +                                            METHOD_NAME__ADR, NULL, &adr);
> > +             if (ACPI_FAILURE(status))
> > +                     return -ENODATA;
>
> Would it make sense to standardize error codes ? of_property_read_u32()
> can return -EINVAL, -ENODATA or -EOVERFLOW. I don't think the caller of
> this function would be very interested to tell those three cases apart.
> Maybe we should return -EINVAL in all error cases ? Or maybe different
> error codes to mean "the backend doesn't support the concept of IDs",
> and "the device doesn't have an ID" ?

We may actually get mapping to all three if first we check for the
method/name existence followed by value check.
But I don't think we need to bloat this simple one.

> > +             *id = (u32)adr;
> > +             return 0;
> > +     }
> > +     return -EINVAL;
> > +}

-- 
With Best Regards,
Andy Shevchenko