linux-kernel - Re: [RFC PATCH 3/3] i2c: i2c-core-of: Handle i2c bus extensions

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Message-ID: <20250212104549.6b1d8781@bootlin.com>
Date: Wed, 12 Feb 2025 10:45:49 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Wolfram Sang <wsa+renesas@...g-engineering.com>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, linux-i2c@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, Luca Ceresoli
 <luca.ceresoli@...tlin.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>
Subject: Re: [RFC PATCH 3/3] i2c: i2c-core-of: Handle i2c bus extensions

Hi Krzysztof,

On Wed, 12 Feb 2025 06:54:19 +0100
Krzysztof Kozlowski <krzk@...nel.org> wrote:

> On 05/02/2025 18:39, Herve Codina wrote:
> >  
> >  	dev_dbg(&adap->dev, "of_i2c: walking child nodes from %pOF\n", bus);
> >  
> > -	/* Register device directly attached to this bus */
> > +	/*
> > +	 * Register device directly described in this bus node before looking
> > +	 * at extensions.
> > +	 */
> >  	for_each_available_child_of_node(bus, node) {
> > +		/* Filter out extension node */
> > +		if (of_node_name_eq(node, "i2c-bus-extension"))  
> 
> Where is the ABI documented?
> 
> > +			continue;
> > +
> >  		if (of_node_test_and_set_flag(node, OF_POPULATED))
> >  			continue;
> >  
> > @@ -103,6 +110,23 @@ static void of_i2c_register_children(struct i2c_adapter *adap,
> >  			of_node_clear_flag(node, OF_POPULATED);
> >  		}
> >  	}
> > +
> > +	/* Look at extensions */
> > +	for_each_available_child_of_node(bus, node) {
> > +		if (!of_node_name_eq(node, "i2c-bus-extension"))
> > +			continue;
> > +
> > +		extension = of_parse_phandle(node, "i2c-bus", 0);  
> 
> And this?
> 
> > +		if (!extension)
> > +			continue;
> > +  

I know the binding is not present in this RFC series.

As I mentioned in my cover letter, the binding that needs to be updated is
available in dt-schema repo [0].

When the binding is be accepted in dt-schema repo, I will not be able to
change it and because two repos are involved, I cannot send the binding and
the implementation in the same series.

Before sending a patch to update the binding in dt-schema repo, I would
like first to discuss the proposed i2c bus extension idea in terms of:
  1) DT properties naming and purpose
  2) implementation

[0] https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/i2c/i2c-controller.yaml

Best regards,
Hervé