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Date:   Fri, 6 May 2022 09:49:05 +0200
From:   =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= <clement.leger@bootlin.com>
To:     Rob Herring <robh@kernel.org>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Nathan Lynch <nathanl@linux.ibm.com>,
        Laurent Dufour <ldufour@linux.ibm.com>,
        Daniel Henrique Barboza <danielhb413@gmail.com>,
        David Gibson <david@gibson.dropbear.id.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Ohhoon Kwon <ohoono.kwon@samsung.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        YueHaibing <yuehaibing@huawei.com>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org,
        Allan Nielsen <allan.nielsen@microchip.com>,
        Horatiu Vultur <horatiu.vultur@microchip.com>,
        Steen Hegelund <steen.hegelund@microchip.com>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH 1/3] of: dynamic: add of_property_alloc() and
 of_property_free()
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        <20220504154033.750511-2-clement.leger@bootlin.com>
        <YnQnayouXw9/jp/E@robh.at.kernel.org>
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Le Thu, 5 May 2022 14:37:15 -0500,
Rob Herring <robh@kernel.org> a =C3=A9crit :


> > +
> > +/**
> > + * of_property_alloc - Allocate a property dynamically.
> > + * @name:	Name of the new property
> > + * @value:	Value that will be copied into the new property value
> > + * @value_len:	length of @value to be copied into the new property val=
ue
> > + * @len:	Length of new property value, must be greater than @value_len=
 =20
>=20
> What's the usecase for the lengths being different? That doesn't seem=20
> like a common case, so perhaps handle it with a NULL value and=20
> non-zero length. Then the caller has to deal with populating=20
> prop->value.

That was actually something used by powerpc code but agreed, letting
the user recopy it's values seems fine to me and the usage will be more
clear.

> >  	/*
> > -	 * NOTE: There is no check for zero length value.
> > -	 * In case of a boolean property, this will allocate a value
> > -	 * of zero bytes. We do this to work around the use
> > -	 * of of_get_property() calls on boolean values.
> > +	 * Even if the property has no value, it must be set to a
> > +	 * non-null value since of_get_property() is used to check
> > +	 * some values that might or not have a values (ranges for
> > +	 * instance). Moreover, when the node is released, prop->value
> > +	 * is kfreed so the memory must come from kmalloc. =20
>=20
> Allowing for NULL value didn't turn out well...
>=20
> We know that we can do the kfree because OF_DYNAMIC is set IIRC...
>=20
> If we do 1 allocation for prop and value, then we can test=20
> for "prop->value =3D=3D prop + 1" to determine if we need to free or not.

Sounds like a good idea.

--=20
Cl=C3=A9ment L=C3=A9ger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com