linux-kernel - Re: [PATCH v4 18/29] i2c: mux: Create missing devlink between mux and adapter physical device

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Message-ID: <6tgbavtf2dqc44ebfighrs5chzx4j4zdmjk77fmulwqbhrex2b@lou7ekbsjekr>
Date: Thu, 30 Oct 2025 16:23:24 +0100
From: Andi Shyti <andi.shyti@...nel.org>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Andrew Lunn <andrew@...n.ch>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
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	Luca Ceresoli <luca.ceresoli@...tlin.com>, Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v4 18/29] i2c: mux: Create missing devlink between mux
 and adapter physical device

Hi Herve,

...

> When an i2c mux is involved in an i2c path, the struct dev topology is
> the following:

supernitpick: I'd leave blank line here.

>     +----------------+                +-------------------+
>     | i2c controller |                |      i2c mux      |
>     |     device     |                |      device       |
>     |       ^        |                |                   |
>     |       |        |                |                   |
>     |  dev's parent  |                |                   |
>     |       |        |                |                   |
>     |   i2c adapter  |                | i2c adapter chanX |
>     |     device  <---- dev's parent ------  device       |
>     |   (no driver)  |                |    (no driver)    |
>     +----------------+                +-------------------+
> 

...

> No relationship exists between the i2c mux device itself and the i2c
> controller device (physical device) in order to have the i2c mux device
> calling i2c_del_adapter() to remove its downtream adapters and so,

/downtream/downstream/

> release references taken to the upstream adapter.

...

> +	/*
> +	 * There is no relationship set between the mux device and the physical
> +	 * device handling the parent adapter. Create this missing relationship
> +	 * in order to remove the i2c mux device (consumer) and so the dowstream
> +	 * channel adapters before removing the physical device (supplier) which
> +	 * handles the i2c mux upstream adapter.
> +	 */
> +	parent_physdev = i2c_get_adapter_physdev(parent);
> +	if (!parent_physdev) {
> +		dev_err(muxc->dev, "failed to get the parent physical device\n");
> +		ret = -EINVAL;

-ENODEV?

> +		goto err_free_priv;
> +	}
> +	dl = device_link_add(muxc->dev, parent_physdev, DL_FLAG_AUTOREMOVE_CONSUMER);

Not to call twice put_device, I would add it once here and then
check for !dl.

> +	if (!dl) {
> +		dev_err(muxc->dev, "failed to create device link to %s\n",
> +			dev_name(parent_physdev));
> +		put_device(parent_physdev);
> +		ret = -EINVAL;

same here, should this be -ENODEV?

Andi

> +		goto err_free_priv;
> +	}
> +	put_device(parent_physdev);
> +
>  	if (force_nr) {
>  		priv->adap.nr = force_nr;
>  		ret = i2c_add_numbered_adapter(&priv->adap);
> -- 
> 2.51.0
>