linux-kernel - Re: [PATCH] input: mtk-pmic-keys: Fix probe when no DT node present

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Message-ID: <20180703091726.GM20176@dell>
Date:   Tue, 3 Jul 2018 10:17:26 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>, chen.zhong@...iatek.com,
        linux-input@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Matthias Brugger <mbrugger@...e.com>
Subject: Re: [PATCH] input: mtk-pmic-keys: Fix probe when no DT node present

On Fri, 22 Jun 2018, Dmitry Torokhov wrote:

> On Fri, Jun 22, 2018 at 01:42:28PM +0200, Matthias Brugger wrote:
> > The drivers gets probed from a mfd devices. So the driver runs
> > probe although no DT node exists. This leads to a NULL pointer
> > dereference in the probe function. Check if a node exists and
> > error out in case none is present.
> 
> Hmm, if a cell specifies of_compatible and no such node is present in DT
> maybe we should bail out in mfd_add_device() instead of pushing the
> check into individual drivers? Something like:
> 
> diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> index 94e3f32ce935..36a5fd98000d 100644
> --- a/drivers/mfd/mfd-core.c
> +++ b/drivers/mfd/mfd-core.c
> @@ -137,6 +137,18 @@ static inline void mfd_acpi_add_device(const struct mfd_cell *cell,
>  }
>  #endif
>  
> +static struct device_node *mfd_get_node_for_cell(struct device *parent,
> +						 const struct mfd_cell *cell)
> +{
> +	struct device_node *np;
> +
> +	for_each_child_of_node(parent->of_node, np)
> +		if (of_device_is_compatible(np, cell->of_compatible))
> +			return np;
> +
> +	return NULL;
> +}
> +
>  static int mfd_add_device(struct device *parent, int id,
>  			  const struct mfd_cell *cell, atomic_t *usage_count,
>  			  struct resource *mem_base,
> @@ -144,7 +156,6 @@ static int mfd_add_device(struct device *parent, int id,
>  {
>  	struct resource *res;
>  	struct platform_device *pdev;
> -	struct device_node *np = NULL;
>  	int ret = -ENOMEM;
>  	int platform_id;
>  	int r;
> @@ -176,11 +187,11 @@ static int mfd_add_device(struct device *parent, int id,
>  		goto fail_res;
>  
>  	if (parent->of_node && cell->of_compatible) {
> -		for_each_child_of_node(parent->of_node, np) {
> -			if (of_device_is_compatible(np, cell->of_compatible)) {
> -				pdev->dev.of_node = np;
> -				break;
> -			}
> +		pdev->dev.of_node = mfd_get_node_for_cell(parent, cell);
> +		if (!pdev->dev.of_node) {
> +			dev_err(parent, "unable to locate node for %s (%s)\n",
> +				cell->name, cell->of_compatible);
> +			goto fail_res;
>  		}
>  	}
>  
> Lee?

This change results the wrong semantics.  MFD overrides Device Tree,
such that if a device is supplied and registered using
mfd_add_device(s) it should be probed.  The only reason we provide a
pointer to the of_node is for the child device to pull properties
from.

If a device should only be probed if an OF node exists, then it should
not be registered at the MFD level.

> > Fixes: 3e9f0b3e2b27 ("input: Add MediaTek PMIC keys support")
> > Signed-off-by: Matthias Brugger <mbrugger@...e.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 02c67a1749fc..388043e1939c 100644
> > --- a/drivers/input/keyboard/mtk-pmic-keys.c
> > +++ b/drivers/input/keyboard/mtk-pmic-keys.c
> > @@ -257,6 +257,9 @@ 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 == NULL)
> > +		return -ENODEV;
> > +
> >  	keys = devm_kzalloc(&pdev->dev, sizeof(*keys), GFP_KERNEL);
> >  	if (!keys)
> >  		return -ENOMEM;
> 
> Thanks.
> 

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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