linux-kernel - Re: [RFC PATCH 07/77] livetree: Improve get_node_by

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Message-ID: <20260116115254.3002ca05@bootlin.com>
Date: Fri, 16 Jan 2026 11:52:54 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: David Gibson <david@...son.dropbear.id.au>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Ayush Singh <ayush@...gleboard.org>,
 Geert Uytterhoeven <geert@...ux-m68k.org>,
 devicetree-compiler@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, devicetree-spec@...r.kernel.org, Hui Pu
 <hui.pu@...ealthcare.com>, Ian Ray <ian.ray@...ealthcare.com>, Luca
 Ceresoli <luca.ceresoli@...tlin.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>
Subject: Re: [RFC PATCH 07/77] livetree: Improve get_node_by_phandle()

Hi David,

On Thu, 15 Jan 2026 11:41:32 +1100
David Gibson <david@...son.dropbear.id.au> wrote:

> On Mon, Jan 12, 2026 at 03:18:57PM +0100, Herve Codina wrote:
> > get_node_by_phandle() allows to get a node based on its phandle value.
> > It checks the phandle value against value available in internal node
> > structure.
> > 
> > This internal phandle value is updated during process_check() and so,
> > get_node_by_phandle() cannot give correct results before the
> > process_check() call.
> > 
> > Improve get_node_by_phandle() to look at node phandle properties when
> > the internal phandle value is not valid.
> > 
> > This allows to return a correct matching node even if process_check()
> > was not called yet.
> > 
> > With the recently introduced FDT_REF_LOCAL dtb tag, this will be needed
> > to update internal phandle references before the call to process_check().
> > Indeed, this tag allows to identify phandles and internal references
> > need to be updated based on the phandle value before the
> > process_check() call.  
> 
> Having two entirely different paths for get_node_by_phandle() is
> really ugly.
> 
> I suspect a better approach would be to special case updates to the
> internal phandle field as we parse the phandle properties, rather than
> doing it as a batch during the checks.

Doing that when we parse the property will be quite complex. Indeed,
when we parse a dts, the node internal object is not yet created when
the property is parsed.

What I think could be done is to set the phandle field just after the
parsing of input (dts or dtb). In current implementation this is done by
process_check() when fixup_phandle_references() is called.

This fixup_phandle_references() call should be removed from process_check()
and called right after the input parsing.

I you are ok with that, I can propose something in the next iteration.

Best regards,
Hervé