linux-kernel - Re: [PATCH] powerpc/sysdev: Use of_device_get_match

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Date:   Fri, 04 Mar 2022 14:26:00 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     "cgel.zte@...il.com" <cgel.zte@...il.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        Zeal Robot <zealci@....com.cn>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Minghao Chi <chi.minghao@....com.cn>,
        "jgg@...pe.ca" <jgg@...pe.ca>,
        "paulus@...ba.org" <paulus@...ba.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] powerpc/sysdev: Use of_device_get_match_data()

On Fri, 04 Mar 2022 13:10:19 +0000,
Christophe Leroy <christophe.leroy@...roup.eu> wrote:
> 
> 
> 
> Le 04/03/2022 à 02:18, cgel.zte@...il.com a écrit :
> > From: Minghao Chi (CGEL ZTE) <chi.minghao@....com.cn>
> > 
> > Use of_device_get_match_data() to simplify the code.
> > 
> > Reported-by: Zeal Robot <zealci@....com.cn>
> > Signed-off-by: Minghao Chi (CGEL ZTE) <chi.minghao@....com.cn>
> > ---
> >   arch/powerpc/sysdev/fsl_msi.c | 6 +-----
> >   1 file changed, 1 insertion(+), 5 deletions(-)
> > 
> > diff --git a/arch/powerpc/sysdev/fsl_msi.c b/arch/powerpc/sysdev/fsl_msi.c
> > index b3475ae9f236..9d135bbb30b7 100644
> > --- a/arch/powerpc/sysdev/fsl_msi.c
> > +++ b/arch/powerpc/sysdev/fsl_msi.c
> > @@ -387,7 +387,6 @@ static int fsl_msi_setup_hwirq(struct fsl_msi *msi, struct platform_device *dev,
> >   static const struct of_device_id fsl_of_msi_ids[];
> >   static int fsl_of_msi_probe(struct platform_device *dev)
> >   {
> > -	const struct of_device_id *match;
> >   	struct fsl_msi *msi;
> >   	struct resource res, msiir;
> >   	int err, i, j, irq_index, count;
> > @@ -397,10 +396,7 @@ static int fsl_of_msi_probe(struct platform_device *dev)
> >   	u32 offset;
> >   	struct pci_controller *phb;
> >   
> > -	match = of_match_device(fsl_of_msi_ids, &dev->dev);
> > -	if (!match)
> > -		return -EINVAL;
> > -	features = match->data;
> > +	features = of_device_get_match_data(&dev->dev);
> 
> What happens when features is NULL ?

I did jump at that one too, but as it turns out, it cannot happen, by
construction. All the fsl_of_msi_ids[] entries have a non-NULL .data
pointer, and you only enter probe if you match a fsl_of_msi_ids[]
entry with the DT.

So the current check for a NULL match is not something that can happen
short of some other bug somewhere.

	M.

-- 
Without deviation from the norm, progress is not possible.