linux-kernel - Re: [PATCH net-next 1/3] device property: Introduce fwnode_for_each_available_child_node

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Message-ID: <Zwj12J5bTNUEnxA0@kekkonen.localdomain>
Date: Fri, 11 Oct 2024 09:54:32 +0000
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Javier Carrasco <javier.carrasco.cruz@...il.com>
Cc: 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>,
	Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 1/3] device property: Introduce
 fwnode_for_each_available_child_node_scoped()

Hi Javier,

On Fri, Oct 11, 2024 at 10:34:32AM +0200, Javier Carrasco wrote:
> On 11/10/2024 07:39, Sakari Ailus wrote:
> > Hi Javier,
> > 
> > On Tue, Oct 08, 2024 at 06:10:27PM +0200, Javier Carrasco wrote:
> >> Introduce the scoped variant of the
> >> fwnode_for_each_available_child_node() to automatically decrement the
> >> child's refcount when it goes out of scope, removing the need for
> >> explicit calls to fwnode_handle_put().
> >>
> >> Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.com>
> >> ---
> >>  include/linux/property.h | 5 +++++
> >>  1 file changed, 5 insertions(+)
> >>
> >> diff --git a/include/linux/property.h b/include/linux/property.h
> >> index 61fc20e5f81f..b37508ecf606 100644
> >> --- a/include/linux/property.h
> >> +++ b/include/linux/property.h
> >> @@ -168,6 +168,11 @@ struct fwnode_handle *fwnode_get_next_available_child_node(
> >>  	for (child = fwnode_get_next_available_child_node(fwnode, NULL); child;\
> >>  	     child = fwnode_get_next_available_child_node(fwnode, child))
> >>  
> >> +#define fwnode_for_each_available_child_node_scoped(fwnode, child)	       \
> >> +	for (struct fwnode_handle *child __free(fwnode_handle) =	       \
> >> +		fwnode_get_next_available_child_node(fwnode, NULL); child;     \
> >> +	     child = fwnode_get_next_available_child_node(fwnode, child))
> >> +
> > 
> > On OF, the implementation of the .get_next_child_node() fwnode op is:
> > 
> > static struct fwnode_handle *
> > of_fwnode_get_next_child_node(const struct fwnode_handle *fwnode,
> >                               struct fwnode_handle *child)
> > {
> >         return of_fwnode_handle(of_get_next_available_child(to_of_node(fwnode),
> >                                                             to_of_node(child)));
> > }
> > 
> > On ACPI we currently have .device_is_available() returning false but that
> > probably should be returning true instead (it's been virtually unused
> > previously).
> > 
> > That makes fwnode_get_next_available_child_node() and
> > fwnode_get_next_child_node() equivalent on both ACPI and OF. Presumably
> > creating unavailable nodes would be useless on swnode, too.
> > 
> > So my question is: what do we gain by adding all these fwnode_*available()
> > helpers?
> > 
> >>  struct fwnode_handle *device_get_next_child_node(const struct device *dev,
> >>  						 struct fwnode_handle *child);
> > 
> 
> Hi Sakari, thanks for your feedback.
> 
> I thought that the difference is not in OF (which either way ends up
> calling __of_device_is_available()), but in ACPI.
> 
> For fwnode_for_each_child_node(), the ACPI callback is
> acpi_get_next_subnode(), and I don't see that the device_is_available()
> callback is used in that case.

fwnode_get_next_available_child_node() also calls
fwnode_device_is_available() and that returns false on all non-device nodes
right now. As noted above, fwnode_device_is_available() should probably
return true for non-device nodes on ACPI. I'll post a patch.

> 
> For fwnode_for_each_available_child_node(),
> fwnode_get_next_available_child_node() is used, which checks
> fwnode_device_is_available(), which then calls device_is_available().
> 
> What's the catch?

-- 
Kind regards,

Sakari Ailus