linux-kernel - Re: [PATCH 2/3] i2c: muxes: i2c-demux-pinctrl: Use of_get_i2c_adapter_by

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Message-ID: <3f702187-8abe-b877-80d0-db95a6ec55da@axentia.se>
Date:   Thu, 19 Oct 2023 11:26:14 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Herve Codina <herve.codina@...tlin.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 2/3] i2c: muxes: i2c-demux-pinctrl: Use
 of_get_i2c_adapter_by_node()

Hi!

2023-10-19 at 09:35, Herve Codina wrote:
> i2c-demux-pinctrl uses the pair of_find_i2c_adapter_by_node() /
> i2c_put_adapter(). These pair alone is not correct to properly lock the
> I2C parent adapter.
> 
> Indeed,	i2c_put_adapter() decrements the module refcount while
> of_find_i2c_adapter_by_node() does not increment it. This leads to an
> overflow over zero of the parent adapter user counter.

Perhaps "... underflow of the parent module refcount."?

> 
> Use the	dedicated function, of_get_i2c_adapter_by_node(), to handle
> correctly the module refcount.
> 
> Signed-off-by: Herve Codina <herve.codina@...tlin.com>

Good find!

Fixes: 50a5ba876908 ("i2c: mux: demux-pinctrl: add driver")
Acked-by: Peter Rosin <peda@...ntia.se>

Cheers,
Peter

> ---
>  drivers/i2c/muxes/i2c-demux-pinctrl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-demux-pinctrl.c b/drivers/i2c/muxes/i2c-demux-pinctrl.c
> index 22f2280eab7f..9f2e4aa28159 100644
> --- a/drivers/i2c/muxes/i2c-demux-pinctrl.c
> +++ b/drivers/i2c/muxes/i2c-demux-pinctrl.c
> @@ -61,7 +61,7 @@ static int i2c_demux_activate_master(struct i2c_demux_pinctrl_priv *priv, u32 ne
>  	if (ret)
>  		goto err;
>  
> -	adap = of_find_i2c_adapter_by_node(priv->chan[new_chan].parent_np);
> +	adap = of_get_i2c_adapter_by_node(priv->chan[new_chan].parent_np);
>  	if (!adap) {
>  		ret = -ENODEV;
>  		goto err_with_revert;