On Tue, 4 Feb 2025 22:54:52 +0530
Ayush Singh <ayush@xxxxxxxxxxxxxxx> wrote:
> > You have perfectly summarized the export-symbols goal and the benefit of
> > this new feature.
> >
> > I am waiting for feedback from other people. I hope we will move forward
> > on this topic and unblock several users (me included) stuck on this real
> > issue.
> >
> > Thanks a lot!
> >
> > Best regards,
> > Hervé
>
> While working on a Patch series to the specification itself, I realized
> that I was missing some edge cases, so wanted to discuss those:
>
> # Scope
>
> Should export-symbols only be used to resolve the properties in parent,
> or should all other children (and their decedents) use the
> `export-symbols` for resolving phandles and path references?
>
> For example, should the following work:
>
>
> parent {
>
> sibling {
>
> led = <&gpio 0 GPIO_ACTIVE_HIGH>
>
> };
>
>
> export-symbols {
>
> gpio = <&my_gpio1>;
>
> };
>
> };
>
>
> This would also mean that bottoms up lookup needs to take place for all
> `export-symbols` that might be present in path to root, before using top
> level `__symbols__` or `/aliases`.
I restricted the use of export-symbols node when an overlay is applied at a node
which contains an export-symbols sub-node.
In your example, If you apply an overlay at parent node, your export-symbols
is used but if you apply an overlay at sibling node, your export-symbols is
not used.
Of course if your overlay applied at parent node looks like the following:
__overlay__ {
sibling {
prop = <&gpio>;
};
};
&gpio will be resolved using your export-symbols. __overlay__ is applied
at parent -> visible in the overlay.
If the base device-tree looks like this:
parent {
sibling {
export-symbols {
gpio = <&my_gpio1>;
};
};
};
The same overlay applied at parent will failed.
Indeed, no export-symbols is available at parent node and so the
gpio symbols used by the overlay will not be resolved even
if an export-symbols exists in the sibling node.
To see this export-symbols from the overlay, the overlay has to be applied
at sibling node and not parent node.
>
>
> # Export symbols phandles
>
> Can export symbols reference each other? For example is the following valid:
>
>
> parent {
>
> export-symbols {
>
> shadow_gpio = <&my_gpio1>;
>
> gpio = <&shadow_gpio>;
>
> };
>
> };
For sure, not planned.
Also, maybe I missed something but I am not sure you can have a
phandle referencing a property.
In your example, shadow_gpio is a property, even if we add a label
to this property i.e.
label_shadow_gpio: shadow_gpio = <&my_gpio1>;
How can we set:
gpio = <&label_shadow_gpio>;
Best regards,
Hervé
