linux-kernel - Re: [PATCH 0/7] of: overlay: Add support for export-symbols node feature

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Message-ID: <bab9f277-a366-48ec-acdd-0896c8307ad9@beagleboard.org>
Date: Tue, 10 Dec 2024 15:26:44 +0530
From: Ayush Singh <ayush@...gleboard.org>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Andrew Davis <afd@...com>, Geert Uytterhoeven <geert@...ux-m68k.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Saravana Kannan <saravanak@...gle.com>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 0/7] of: overlay: Add support for export-symbols node
 feature

On 10/12/24 15:11, Herve Codina wrote:
> Hi Ayush,
> 
> On Tue, 10 Dec 2024 14:52:22 +0530
> Ayush Singh <ayush@...gleboard.org> wrote:
> 
> ...
>>
>> What is the reason for not using symbols directly as described here [3]?
>>
>> I do like this approach since it does not pollute the global symbols.
>> Just want to know if there are any other reasons for it.
>>
> 
> Modifying the __symbols__ node at runtime (adding / removing properties in
> it) exposes memory leaks if __symbols__ already exist in the live DT.
> This __symbols__ node exist if the dtb was compiled with '-@' or if you
> chain the overlay (i.e. __symbols__ node created by the first overlay).

Yeah, that is a problem, specially in a setup which might involve 
hot-plugging.

> 
> I think also that some conflicts can appears. What happens if you want to
> add a new label but this label is already present for some other purpose?

I do not think that actually is a problem. As described in the original 
patch [0], the symbol and connector overlay is supposed to be applied as 
a group (overwriting any conflicting symbols in the process).

The reason why this is not a problem is that `__symbols__` are only used 
to resolve the phandles (overlays do not support path references yet), 
but do not really have a purpose in the livetree (at least far as I 
know, but I can be wrong).

> 
> Best regards,
> Hervé

[0]: https://lore.kernel.org/lkml/20240702164403.29067-1-afd@ti.com/

Ayush Singh