Re: [PATCH 1/2] libfdt: overlay: Allow resolving phandle symbols

[Ayush Singh <ayush@beagleboard.org>]

On 9/23/24 15:18, David Gibson wrote:

> On Mon, Sep 23, 2024 at 11:12:02AM +0200, Geert Uytterhoeven wrote:
>> Hi David,
>>
>> On Mon, Sep 23, 2024 at 10:41 AM David Gibson
>> <david@gibson.dropbear.id.au> wrote:
>>> On Mon, Sep 23, 2024 at 10:22:03AM +0200, Geert Uytterhoeven wrote:
>>>> On Mon, Sep 23, 2024 at 5:41 AM David Gibson
>>>> <david@gibson.dropbear.id.au> wrote:
>>>>> So, essentially you're just adding new labels as aliases to existing
>>>>> labels?
>>>>>
>>>>> Ok, I can see at least two ways of doing that which I think are a more
>>>>> natural fit than allowing symbols to be phandles.
>>>> [...]
>>>>
>>>>> # Method 2: /aliases
>>>> Does the (Linux) DT overlay code support updating aliases?
>>>> Last time I needed that (almost a decade ago), it did not.
>>> Huh.  I hadn't realised the kernel kept a separate cache of aliases
>>> that wasn't updated.  Assuming that's still the case, that would
>>> complicate matters a bit.
>> Indeed.
> Actually, in a sense this is just an aspect of a more general thing:
> libfdt's is not the only relevant implementation of overlays.  If you
> want to extend what overlays can do, you need to consider the kernel
> implementation too.
>

So, I don't think we can go the aliases route. I posted an updated  
of_alias patch [0], but as Rob pointed out:

```

Drivers use the non-existent alias numbers for instances without an
alias. So what happens if an index is already in use and then an
overlay uses the same index.

I don't see how this can work reliably unless the alias name doesn't
exist in the base DT.

```


Not really sure how alias overloading can be supported in kernel without 
breaking existing drivers.

Overlays are starting to feel more like a hack the longer I work on this.


I guess I can try out implementing `foo = &bar;` approach and see how 
that goes.


[0]: 
https://lore.kernel.org/all/20241110-of-alias-v2-0-16da9844a93e@beagleboard.org/T/#t


Ayush Singh