linux-kernel - Re: [PATCH v2] media: i2c: thp7312: use fwnode_for_each_child

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Message-ID: <Z-El2EzbV5EFDA3Q@kekkonen.localdomain>
Date: Mon, 24 Mar 2025 09:28:56 +0000
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Matti Vaittinen <mazziesaccount@...il.com>,
	Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
	Paul Elder <paul.elder@...asonboard.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v2] media: i2c: thp7312: use fwnode_for_each_child_node()

Hi Laurent,

On Fri, Mar 21, 2025 at 12:41:00PM +0200, Laurent Pinchart wrote:
> Hi Matti,
> 
> Thank you for the patch.
> 
> On Fri, Mar 21, 2025 at 10:58:27AM +0200, Matti Vaittinen wrote:
> > When fwnode_for_each_available_child_node() is used on the device-tree
> > backed systems, it renders to same operation as the
> > fwnode_for_each_child_node(), because the fwnode_for_each_child_node()
> > does only iterate through those device-tree nodes which are available.
> 
> This makes me wonder why the OF backend implements
> fwnode_for_each_child_node() as fwnode_for_each_available_child_node().
> Is that on purpose, or is it a bug ?

I went back to see where this came from,I understand
<URL:https://lkml.org/lkml/2014/10/17/185> is the first version of the
patch adding device_get_next_child_node(). Since then the behaviour has
been carried forward.

Cc Rafael.

> 
> > The thp7312 uses the fwnode_for_each_available_child_node() to look up
> > and handle nodes with specific names. This means the code is used only
> > on the device-tree backed systems because the node names have little
> > meaning on ACPI or swnode backed systems.
> > 
> > Use the fwnode_for_each_child_node() instead of the
> > fwnode_for_each_available_child_node() In order to make it clearly
> > visible that the 'availability' of the nodes does not need to be
> > explicitly considered here. This will also make it clearly visible that
> > the code in this driver is suitable candidate to be converted to use the
> > new fwnode_for_each_named_child_node()[2] when it gets merged.
> > 
> > [1]: https://lore.kernel.org/all/Z9rhfJUlCbi7kA2m@kekkonen.localdomain/
> > [2]: https://lore.kernel.org/all/9c3880f74476436f39d796b5c10c540ae50b722c.1742225817.git.mazziesaccount@gmail.com/
> > 
> > Suggested-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> > 
> > ---
> > Revision history:
> > v1 => v2:
> >  - rephrase the commit message to not claim the 'availability' has no
> >    well defined meaning on the DT backed systems. Instead, explain that
> >    the fwnode_for_each_available_child_node() only iterates through the
> >    available nodes on the DT backed systems and is thus functionally
> >    equivalent to the fwnode_for_each_child_node().
> > 
> > NOTE: The change is compile tested only! Proper testing and reviewing is
> > highly appreciated (as always).
> > ---
> >  drivers/media/i2c/thp7312.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/i2c/thp7312.c b/drivers/media/i2c/thp7312.c
> > index 8852c56431fe..4b66f64f8d65 100644
> > --- a/drivers/media/i2c/thp7312.c
> > +++ b/drivers/media/i2c/thp7312.c
> > @@ -2067,7 +2067,7 @@ static int thp7312_parse_dt(struct thp7312_device *thp7312)
> >  		return -EINVAL;
> >  	}
> >  
> > -	fwnode_for_each_available_child_node(sensors, node) {
> > +	fwnode_for_each_child_node(sensors, node) {
> >  		if (fwnode_name_eq(node, "sensor")) {
> >  			if (!thp7312_sensor_parse_dt(thp7312, node))
> >  				num_sensors++;
> > 
> > base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6
> 

-- 
Kind regards,

Sakari Ailus