linux-kernel - Re: [PATCH RFC] of: Add of_parse_map_iter() helper for nexus node map iteration

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Message-ID: <20251125085521.451ea208@bootlin.com>
Date: Tue, 25 Nov 2025 08:55:21 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Kevin Hilman <khilman@...libre.com>
Cc: Rob Herring <robh@...nel.org>, Ulf Hansson <ulf.hansson@...aro.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, devicetree@...r.kernel.org,
 linux-pm@...r.kernel.org, arm-scmi@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] of: Add of_parse_map_iter() helper for nexus node
 map iteration

Hi Kevin,

On Mon, 24 Nov 2025 17:50:11 -0800
Kevin Hilman <khilman@...libre.com> wrote:

> >
> > There's also this in flight for interrupt-map:
> >
> > https://lore.kernel.org/all/20251027123601.77216-2-herve.codina@bootlin.com/
> >
> > There's probably enough quirks with interrupt-map that we can't use
> > the same code. Though it may boil down to handling #address-cells and
> > how the parent is looked up.  
> 
> Hmm, I wasn't aware of this, thanks for point it out.  It looks very
> similar to what i need, except for it's hard-coding the properties as
> "#interrupt-*".
> 
> Seems like this should be generalized to handle the generic nexus-node
> map. But it also seems to rely on an existing function
> of_irq_parse_imap_parent() which is also specific to interrupt maps.
> 
> That being said, I'm not sure if interrupt-maps are really special, or
> if they are just a specific case of the nexus node map.  This drivers/of
> code is breaking my brain, so it's more likely that I simply don't
> understand enough of it to know how to do this correctly.
> 

The main difference between interrupt-map [1] and the other nexus node maps
is that in interrupt-map a child unit address is involved and translated to
the parent unit address of the matched interrupt-map item.

This child unit address is simply not present in other nexus node maps [2].

[1] https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#interrupt-map
[2] https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#nexus-node-properties

Best regards,
Hervé