linux-kernel - Re: [PATCH v3 1/7] i2c: mux: add the ability to share mux address with child nodes

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Date: Tue, 11 Jun 2024 20:01:59 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Farouk Bouabid <farouk.bouabid@...rry.de>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>,
 Peter Rosin <peda@...ntia.se>, Andi Shyti <andi.shyti@...nel.org>,
 Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Quentin Schulz
 <quentin.schulz@...rry.de>, Heiko Stuebner <heiko@...ech.de>
Cc: linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v3 1/7] i2c: mux: add the ability to share mux address
 with child nodes

Le 11/06/2024 à 13:43, Farouk Bouabid a écrit :
> Allow the mux (if it's an I2C device) to have the same address as a child
> device. This is useful when the mux can only use an I2C address that is
> used by a child device because no other addresses are free to use.
> eg. the mux can only use address 0x18 which is used by amc6821 connected
> to the mux.
> 
> Signed-off-by: Farouk Bouabid <farouk.bouabid@...rry.de>
> ---

Hi,

2 nitpicks below.

> --- a/drivers/i2c/i2c-mux.c
> +++ b/drivers/i2c/i2c-mux.c
> @@ -334,7 +334,53 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
>   	priv->adap.dev.parent = &parent->dev;
>   	priv->adap.retries = parent->retries;
>   	priv->adap.timeout = parent->timeout;
> -	priv->adap.quirks = parent->quirks;
> +
> +	struct i2c_adapter_quirks *quirks;

Should this be at the beginning of the function?

> +	/*
> +	 * When creating the adapter, the node devices are checked for I2C address
> +	 * match with other devices on the parent adapter, among which is the mux itself.
> +	 * If a match is found the node device is not probed successfully.
> +	 * Allow the mux to have the same address as a child device by skipping this check.
> +	 */
> +	if (muxc->share_addr_with_children) {
> +		struct i2c_client *client = to_i2c_client(muxc->dev);
> +
> +		if (muxc->dev->type != &i2c_client_type)
> +			dev_warn_once(muxc->dev, "Mux is not an I2C device\n");
> +
> +		quirks = devm_kzalloc(muxc->dev, sizeof(*quirks), GFP_KERNEL);
> +		if (!quirks)
> +			return -ENOMEM;
> +
> +		if (parent->quirks)
> +			memcpy(quirks, parent->quirks, sizeof(*quirks));
> +
> +		quirks->flags |= I2C_AQ_SKIP_ADDR_CHECK;
> +		quirks->skip_addr_in_parent = client->addr;
> +		priv->adap.quirks = quirks;
> +
> +	} else if (parent->quirks &&
> +		   parent->quirks->flags & I2C_AQ_SKIP_ADDR_CHECK) {
> +		/*
> +		 * Another I2C mux device can be a child of the Mule I2C mux.
> +		 * The former could probably not allow address conflict between
> +		 * its address and its own children addresses.
> +		 *
> +		 * For this purpose, do not propagate this flag unless
> +		 * share_addr_with_children is set.
> +		 */
> +		quirks = devm_kzalloc(muxc->dev, sizeof(*quirks), GFP_KERNEL);

devm_kmemdup()? (not sure it is a win)

> +		if (!quirks)
> +			return -ENOMEM;
> +
> +		memcpy(quirks, parent->quirks, sizeof(*quirks));
> +		quirks->flags &= ~I2C_AQ_SKIP_ADDR_CHECK;
> +		priv->adap.quirks = quirks;
> +
> +	} else {
> +		priv->adap.quirks = parent->quirks;
> +	}
> +
>   	if (muxc->mux_locked)
>   		priv->adap.lock_ops = &i2c_mux_lock_ops;
>   	else

...

CJ