linux-kernel - Re: [PATCH] powermac: Use of_property_match_string() in pmac_has_backlight

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Message-ID: <e50907a9-6df7-4cbf-97a6-47acd5d8ce01@stanley.mountain>
Date: Sun, 13 Oct 2024 16:41:08 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Markus Elfring <Markus.Elfring@....de>, linuxppc-dev@...ts.ozlabs.org,
	Jani Nikula <jani.nikula@...el.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Naveen N Rao <naveen@...nel.org>,
	Nicholas Piggin <npiggin@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH] powermac: Use of_property_match_string() in
 pmac_has_backlight_type()

On Fri, Oct 11, 2024 at 06:25:45PM +0200, Christophe Leroy wrote:
> > diff --git a/arch/powerpc/platforms/powermac/backlight.c b/arch/powerpc/platforms/powermac/backlight.c
> > index 12bc01353bd3..79741370c40c 100644
> > --- a/arch/powerpc/platforms/powermac/backlight.c
> > +++ b/arch/powerpc/platforms/powermac/backlight.c
> > @@ -57,18 +57,10 @@ struct backlight_device *pmac_backlight;
> >   int pmac_has_backlight_type(const char *type)
> >   {
> >   	struct device_node* bk_node = of_find_node_by_name(NULL, "backlight");
> > +	int i = of_property_match_string(bk_node, "backlight-control", type);
> > 
> > -	if (bk_node) {
> > -		const char *prop = of_get_property(bk_node,
> > -				"backlight-control", NULL);
> > -		if (prop && strncmp(prop, type, strlen(type)) == 0) {
> > -			of_node_put(bk_node);
> > -			return 1;
> > -		}
> > -		of_node_put(bk_node);
> > -	}
> > -
> > -	return 0;
> > +	of_node_put(bk_node);
> > +	return i >= 0;
> 
> Could have been:
> 
> 	return !IS_ERR_VALUE(i);
> 

IS_ERR_VALUE() macro should only be used when you're dealing with memory
addresses.  What I mean is there places in mm/ where we pass addresses as
unsigned long values instead of pointers.  For example, get_unmapped_area()
returns unsigned long.  The IS_ERR_VALUE() macro is necessary for that.

For regular error codes, we can just check for negatives.  we don't have do
anything fancy.

Of course, you can find counter examples, like msm_iommu_attach_dev() or
st_fdma_of_xlate().  <small joke>But in those cases, it's done to deliberately
to ensure that the code will never accidentally get built on 64bit systems.
</small joke>

regards,
dan carpenter