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

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Message-ID: <875z05y4a2.fsf@baylibre.com>
Date:   Thu, 29 Apr 2021 08:48:53 +0200
From:   Mattijs Korpershoek <mkorpershoek@...libre.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.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 Dmitry,

Dmitry Torokhov <dmitry.torokhov@...il.com> writes:

> 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.

You are right. Maybe I can fix MFD core instead. I will look into it.

Thanks for your review.
>
>> 
>> 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