linux-kernel - Re: [PATCH v2 3/3] hwmon: (ltc2992) Use fwnode_for_each_available_child_node

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Date: Mon, 27 May 2024 17:30:10 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Javier Carrasco <javier.carrasco.cruz@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Jean Delvare <jdelvare@...e.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Antoniu Miclaus <antoniu.miclaus@...log.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hwmon@...r.kernel.org, Rob Herring <robh@...nel.org>,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2 3/3] hwmon: (ltc2992) Use
 fwnode_for_each_available_child_node_scoped()

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@...il.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@...ux.intel.com>
> > Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.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