Re: [RFC PATCH 2/5] of: Introduce for_each_child_of_node_scoped() to automate of_node_put() handling

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Rob Herring <robh@kernel.org>
Cc: "David Lechner" <dlechner@baylibre.com>,
	"Jonathan Cameron" <jic23@kernel.org>,
	linux-iio@vger.kernel.org,
	"Frank Rowand" <frowand.list@gmail.com>,
	linux-kernel@vger.kernel.org,
	"Julia Lawall" <Julia.Lawall@inria.fr>,
	"Nicolas Palix" <nicolas.palix@imag.fr>,
	"Sumera Priyadarsini" <sylphrenadin@gmail.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	"Len Brown" <lenb@kernel.org>,
	linux-acpi@vger.kernel.org,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Nuno Sá" <nuno.sa@analog.com>
Subject: Re: [RFC PATCH 2/5] of: Introduce for_each_child_of_node_scoped() to automate of_node_put() handling
Date: Thu, 1 Feb 2024 15:17:00 +0000	[thread overview]
Message-ID: <20240201151700.000038ee@Huawei.com> (raw)
In-Reply-To: <20240131235148.GA2743404-robh@kernel.org>

On Wed, 31 Jan 2024 17:51:48 -0600
Rob Herring <robh@kernel.org> wrote:

> On Sun, Jan 28, 2024 at 03:11:01PM -0600, David Lechner wrote:
> > On Sun, Jan 28, 2024 at 10:06 AM Jonathan Cameron <jic23@kernel.org> wrote:  
> > >
> > > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > >
> > > To avoid issues with out of order cleanup, or ambiguity about when the
> > > auto freed data is first instantiated, do it within the for loop definition.
> > >
> > > The disadvantage is that the struct device_node *child variable creation
> > > is not immediately obvious where this is used.
> > > However, in many cases, if there is another definition of
> > > struct device_node *child; the compiler / static analysers will notify us
> > > that it is unused, or uninitialized.
> > >
> > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > ---
> > >  include/linux/of.h | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > >
> > > diff --git a/include/linux/of.h b/include/linux/of.h
> > > index 50e882ee91da..f822226eac6d 100644
> > > --- a/include/linux/of.h
> > > +++ b/include/linux/of.h
> > > @@ -1434,6 +1434,12 @@ static inline int of_property_read_s32(const struct device_node *np,
> > >         for (child = of_get_next_available_child(parent, NULL); child != NULL; \
> > >              child = of_get_next_available_child(parent, child))
> > >
> > > +#define for_each_child_of_node_scoped(parent, child) \
> > > +       for (struct device_node *child __free(device_node) =            \
> > > +            of_get_next_child(parent, NULL);                           \
> > > +            child != NULL;                                             \
> > > +            child = of_get_next_available_child(parent, child))  
> > 
> > Doesn't this need to match the initializer (of_get_next_child)?
> > Otherwise it seems like the first node could be a disabled node but no
> > other disabled nodes would be included in the iteration.
> > 
> > It seems like we would want two macros, one for each variation,
> > analogous to for_each_child_of_node() and
> > for_each_available_child_of_node().  
> 
> Yes, but really I'd like these the other way around. 'available' should 
> be the default as disabled should really be the same as a node not 
> present except for a few cases where it is not.
> 
> I bring it up only because if we're changing things then it is a 
> convenient time to change this. That's really a side issue to sorting 
> out how this new way should work.

Happy to push that forwards by not initially defining the non available version
of this scoped form. So we will just have

for_each_avaiable_child_of_node_scoped()

Short and snappy it isn't but such is life.

Jonathan

> 
> Rob
> 