linux-kernel - Re: [PATCH v4 02/10] property: Add device_get_child_node_count

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Message-ID: <44b1cc7f-a5e1-4c61-8b9c-1ba0c51e6343@gmail.com>
Date: Sun, 2 Mar 2025 14:22:55 +0200
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Rob Herring <robh@...nel.org>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
 Jonathan Cameron <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...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>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>,
 Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
 Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Samuel Holland <samuel@...lland.org>,
 Hugo Villeneuve <hvilleneuve@...onoff.com>, Nuno Sa <nuno.sa@...log.com>,
 David Lechner <dlechner@...libre.com>,
 Javier Carrasco <javier.carrasco.cruz@...il.com>,
 Guillaume Stols <gstols@...libre.com>,
 Olivier Moysan <olivier.moysan@...s.st.com>,
 Dumitru Ceclan <mitrutzceclan@...il.com>,
 Trevor Gamblin <tgamblin@...libre.com>,
 Matteo Martelli <matteomartelli3@...il.com>,
 Alisa-Dariana Roman <alisadariana@...il.com>,
 Ramona Alexandra Nechita <ramona.nechita@...log.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH v4 02/10] property: Add
 device_get_child_node_count_named()

On 28/02/2025 19:07, Rob Herring wrote:
> On Mon, Feb 24, 2025 at 12:33 PM Matti Vaittinen
> <mazziesaccount@...il.com> wrote:
>>
>> There are some use-cases where child nodes with a specific name need to
>> be parsed. In a few cases the data from the found nodes is added to an
>> array which is allocated based on the number of found nodes. One example
>> of such use is the IIO subsystem's ADC channel nodes, where the relevant
>> nodes are named as channel[@N].
>>
>> Add a helper for counting device's sub-nodes with certain name instead
>> of open-coding this in every user.
>>
>> Suggested-by: Jonathan Cameron <jic23@...nel.org>
>> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
>> ---
>> Revision history:
>> v3 => v4:
>>   - New patch as suggested by Jonathan, see discussion in:
>> https://lore.kernel.org/lkml/20250223161338.5c896280@jic23-huawei/
>> ---
>>   drivers/base/property.c  | 28 ++++++++++++++++++++++++++++
>>   include/linux/property.h |  2 ++
>>   2 files changed, 30 insertions(+)
>>
>> diff --git a/drivers/base/property.c b/drivers/base/property.c
>> index c1392743df9c..3f85818183cd 100644
>> --- a/drivers/base/property.c
>> +++ b/drivers/base/property.c
>> @@ -945,6 +945,34 @@ unsigned int device_get_child_node_count(const struct device *dev)
>>   }
>>   EXPORT_SYMBOL_GPL(device_get_child_node_count);
>>
>> +/**
>> + * device_get_child_node_count_named - number of child nodes with given name
>> + *
>> + * Scan device's child nodes and find all the nodes with a specific name and
>> + * return the number of found nodes. Potential '@...ber' -ending for scanned
>> + * names is ignored. Eg,
>> + * device_get_child_node_count(dev, "channel");
>> + * would match all the nodes:
>> + * channel { }, channel@0 {}, channel@...bba {}...
>> + *
>> + * @dev: Device to count the child nodes for
>> + *
>> + * Return: the number of child nodes with a matching name for a given device.
>> + */
>> +unsigned int device_get_child_node_count_named(const struct device *dev,
>> +                                              const char *name)
> 
> I think this should be implemented as
> fwnode_get_child_node_count_named() with the device variant being just
> a wrapper.

I thought of that but it'll mean we had two very little used APIs 
instead of just one. Well, perhaps we see new users though so I'll 
follow this suggestion for v5.

Yours,
	-- Matti