linux-kernel - Re: [RFC PATCH 09/77] dtc: Introduce mark_local

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Message-ID: <20260116140912.3d18ae39@bootlin.com>
Date: Fri, 16 Jan 2026 14:09:12 +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 09/77] dtc: Introduce mark_local_phandles()

Hi David,

On Thu, 15 Jan 2026 11:48:44 +1100
David Gibson <david@...son.dropbear.id.au> wrote:

> On Mon, Jan 12, 2026 at 03:18:59PM +0100, Herve Codina wrote:
> > In order to have the new FDT_REF_LOCAL tag present in a dtb, the phandle
> > reference needs to be identify as a local reference.
> > 
> > This is the purpose of mark_local_phandles().
> > 
> > It identifies a phandle reference as a local reference when this
> > reference points to a local node.
> > 
> > With that node, the related FDT_REF_LOCAL tag is set in the dtb.  
> 
> I dislike caching redundant information (whether the ref is local) -
> it's an opportunity for them to get out of sync and cause bugs.  Is
> there a strong case that you can't just determine whether it's local
> only when you actually go to use it?

Well, I can't find any strong case.

I would like to avoid passing the full dti (struct dt_info) to flatten_tree()
in order to determine if the ref is local or not to set a FDT_REF_LOCAL or
a FDT_REF_PHANDLE tag.

Also, this flag, set when a FDT_REF_LOCAL tag is parsed from a dtb, is
useful later when the ref has to be found based on the phandle value.

Indeed, because the is_local flag is set, the phandle value available in the
property *must* reference an existing node in the dtb.

In other word, in update_phandles_ref_internal(), 
--- 8< ---
	if (m->is_local) {
		phandle = propval_cell_n(prop,
					 m->offset / sizeof(cell_t));
		refnode = dti_get_node_by_phandle(dti, phandle);
		if (!refnode)
			die("Node not found for phandle 0x%"PRIx32"\n", phandle);

		m->ref = refnode->fullpath;
		continue;
	} else {
		...
--- 8< ---

Best regards,
Hervé