linux-kernel - Re: [PATCH 1/7] Input: mtk-pmic-keys - check for NULL on of_match

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Date:   Wed, 28 Apr 2021 12:52:37 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Mattijs Korpershoek <mkorpershoek@...libre.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>, fparent@...libre.com,
        linux-input@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] Input: mtk-pmic-keys - check for NULL on
 of_match_device()

Hi Mattijs,

On Wed, Apr 28, 2021 at 06:42:13PM +0200, Mattijs Korpershoek wrote:
> mtk-pmic-keys being a child device of mt6397, it will always get probed
> when mt6397_probe() is called.
> 
> This also happens when we have no device tree node matching
> mediatek,mt6397-keys.

It sounds for me that creating a platform device instance in case where
we know need OF node, but do not have one, is wasteful. Can
mt6397-core.c and/or MFD core be adjusted to not do that.

> 
> In that case, the mfd core warns us:
> 
>   [    0.352175] mtk-pmic-keys: Failed to locate of_node [id: -1]
> 
> Check return value from call to of_match_device()
> in order to prevent a NULL pointer dereference.
> 
> In case of NULL print error message and return -ENODEV
> 
> Signed-off-by: Mattijs Korpershoek <mkorpershoek@...libre.com>
> ---
>  drivers/input/keyboard/mtk-pmic-keys.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/input/keyboard/mtk-pmic-keys.c b/drivers/input/keyboard/mtk-pmic-keys.c
> index 62391d6c7da6..12c449eed026 100644
> --- a/drivers/input/keyboard/mtk-pmic-keys.c
> +++ b/drivers/input/keyboard/mtk-pmic-keys.c
> @@ -247,6 +247,9 @@ static int mtk_pmic_keys_probe(struct platform_device *pdev)
>  	const struct of_device_id *of_id =
>  		of_match_device(of_mtk_pmic_keys_match_tbl, &pdev->dev);
>  
> +	if (!of_id)
> +		return -ENODEV;
> +

So if we make MFD/6396 core smarter we would not be needing this. I
guess there is still a possibility of someone stuffing "mtk-pmic-keys"
into "driver_override" attribute of a random platform device but I
wonder if we really need to take care of such scenarios...

>  	keys = devm_kzalloc(&pdev->dev, sizeof(*keys), GFP_KERNEL);
>  	if (!keys)
>  		return -ENOMEM;
> -- 
> 2.27.0
> 

Thanks.

-- 
Dmitry