Received-SPF: pass (google.com: domain of linux-kernel+bounces-190978-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
From: Andy Shevchenko <andy.shevchenko@gmail.com>
Date: Mon, 27 May 2024 17:30:10 +0300
To: Jonathan Cameron <jic23@kernel.org>
Cc: Javier Carrasco <javier.carrasco.cruz@gmail.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Daniel Scally <djrscally@gmail.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Jean Delvare <jdelvare@suse.com>,
	Guenter Roeck <linux@roeck-us.net>,
	Antoniu Miclaus <antoniu.miclaus@analog.com>,
	linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-hwmon@vger.kernel.org, Rob Herring <robh@kernel.org>,
	devicetree@vger.kernel.org
Subject: Re: [PATCH v2 3/3] hwmon: (ltc2992) Use
 fwnode_for_each_available_child_node_scoped()
Message-ID: <ZlSY8tjYm5g9bEJ_@surfacebook.localdomain>
References: <20240523-fwnode_for_each_available_child_node_scoped-v2-0-701f3a03f2fb@gmail.com>
 <20240523-fwnode_for_each_available_child_node_scoped-v2-3-701f3a03f2fb@gmail.com>
 <20240526144851.493dd3f2@jic23-huawei>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240526144851.493dd3f2@jic23-huawei>

Sun, May 26, 2024 at 02:48:51PM +0100, Jonathan Cameron kirjoitti:
> On Thu, 23 May 2024 17:47:16 +0200
> Javier Carrasco <javier.carrasco.cruz@gmail.com> wrote:
> 
> > The scoped version of the fwnode_for_each_available_child_node() macro
> > automates object recfount decrement, avoiding possible memory leaks
> > in new error paths inside the loop like it happened when
> > commit '10b029020487 ("hwmon: (ltc2992) Avoid division by zero")'
> > was added.
> > 
> > The new macro removes the need to manually call fwnode_handle_put() in
> > the existing error paths and in any future addition. It also removes the
> > need for the current child node declaration as well, as it is internally
> > declared.
> > 
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
> 
> This looks like another instances of the lack of clarify about 
> what device_for_each_child_node[_scoped]() guarantees about node availability.
> On DT it guarantees the node is available as ultimately calls
> of_get_next_available_child()
> 
> On ACPI it doesn't (I think).
> For swnode, there isn't an obvious concept of available.
> 
> It would be much better if we reached some agreement on this and
> hence could avoid using the fwnode variants just to get the _available_ form
> as done here.

> Or just add the device_for_each_available_child_node[_scoped]()
> and call that in almost all cases.

device_for_each*() _implies_ availability. You need to talk to Rob about all
this. The design of the device_for_each*() was exactly done in accordance with
his suggestions...

> In generic code, do we ever want to walk unavailable child nodes?

..which are most likely like your question here, i.e. why we ever need to
traverse over unavailable nodes.


-- 
With Best Regards,
Andy Shevchenko