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

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Message-ID: <Z_UDmqZoPtybJr95@kekkonen.localdomain>
Date: Tue, 8 Apr 2025 11:08:10 +0000
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.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
Subject: Re: [PATCH v2] media: i2c: thp7312: use fwnode_for_each_child_node()

Moi,

On Tue, Apr 08, 2025 at 01:42:12PM +0300, Matti Vaittinen wrote:
> On 08/04/2025 13:36, Sakari Ailus wrote:
> > Hei Laurent, Matti,
> > 
> > On Tue, Apr 08, 2025 at 01:26:42PM +0300, Matti Vaittinen wrote:
> > > On 08/04/2025 13:12, Laurent Pinchart wrote:
> > > > Hi Sakari,
> > > > 
> > > > On Tue, Apr 08, 2025 at 08:48:45AM +0000, Sakari Ailus wrote:
> > > > > On Fri, Mar 21, 2025 at 12:41:00PM +0200, Laurent Pinchart wrote:
> > > > > > 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 discussed this with Rafael and he didn't recall why the original
> > > > > implementation was like that. The general direction later on has been not
> > > > > to present unavailable nodes over the fwnode interface.
> > > > > 
> > > > > So I'd say:
> > > > > 
> > > > > Reviewed-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > > > > 
> > > > > We should also change the documentation of the fwnode API accordingly.
> > > > 
> > > > Does that also mean that the fwnode_for_each_available_child_node()
> > > > function will be dropped ? It's used by few drivers (5 in addition to
> > > > the thp7312 driver, plus 3 call sites in drivers/base/core.c), so a
> > > > patch series to drop it should be easy.
> > > > 
> > > 
> > > I assume the fwnode_for_each_available_child_node() still makes sense for
> > > ACPI backed users, no?
> > 
> > Not really (see my earlier explanation in
> > <Z9mQPJwnKAkPHriT@...konen.localdomain>).
> 
> I capture that the _named_ available nodes don't have value as ACPI names
> aren't really what is expected by the _named_ callers. What I didn't pick is
> that the fwnode_for_each_available_child_node() - which should iterate all
> available child nodes ignoring the name - wouldn't be useful.

Fair enough. I don't think we need to support enumerating unavailable ACPI
device nodes in this API. I'd indeed change the behaviour so that only
available nodes are enumerated. I can post a patch for that.

> 
> > I think all the *available* stuff
> > should be removed from include/linux/property.h, apart from
> > fwnode_device_is_availble(), which should be turned to work on struct
> > device to signal its availability for device nodes only.
> 
> I am not saying I have any understanding of the uses of the 'unavailable'
> nodes. As such I am not arguing over what you say here :)

-- 
Kind regards,

Sakari Ailus