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

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Message-ID: <20250108104719.0412ad94@bootlin.com>
Date: Wed, 8 Jan 2025 10:47:19 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Ayush Singh <ayush@...gleboard.org>
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>, David Gibson
 <david@...son.dropbear.id.au>
Subject: Re: [PATCH 0/7] of: overlay: Add support for export-symbols node
 feature

Hi Ayush,

On Wed, 8 Jan 2025 13:58:04 +0530
Ayush Singh <ayush@...gleboard.org> wrote:

...
> 
> I will experiment with adding support to dtc and see how things look. 
> Hopefully, 2025 is the year of addon board support.
> 

Also one point different between fdtoverlay an runtime loading is
that runtime loading allows to set the target node of the overlay
at runtime.

For instance, on LAN966X PCI driver, an overlay is loaded and
applied on a PCI device node.
The overlay loading is done by the PCI driver device:
  https://elixir.bootlin.com/linux/v6.13-rc1/source/drivers/misc/lan966x_pci.c#L131
The overlay loaded is the following one:
  https://elixir.bootlin.com/linux/v6.13-rc1/source/drivers/misc/lan966x_pci.dtso

For addon boards, this feature is also useful because without any
modification in the overlay itself, it can be applied on the correct
connector. This allows to support, without any overlay modification the
following cases:
 - A base board with multiple connectors where an addon board can be
   connected.
 - An addon board with its own DT overlay used on different base board

This feature is not supported by fdtoverlay. Maybe something like
  fdtoverlay --base=/somewhere/my_connector
could be implemented in fdtoverlay in order to choose the node where the
overlay has to be applied.

Best regards,
Hervé