Re: [PATCH v8 02/10] property: Add functions to iterate named child

[Matti Vaittinen <mazziesaccount@gmail.com>]

Moro Sakari,

Thanks for the review.

On 18/03/2025 17:24, Sakari Ailus wrote:
> Moi,
> 
> On Mon, Mar 17, 2025 at 05:50:38PM +0200, Matti Vaittinen wrote:
>> There are a few use-cases where child nodes with a specific name need to
>> be parsed. Code like:
>>
>> fwnode_for_each_child_node()
>> 	if (fwnode_name_eq())
>> 		...
>>
>> can be found from a various drivers/subsystems. Adding a macro for this
>> can simplify things a bit.
>>
>> In a few cases the data from the found nodes is later 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 helpers for iterating and counting device's sub-nodes with certain
>> name instead of open-coding this in every user.
>>
>> Suggested-by: Jonathan Cameron <jic23@kernel.org>
>> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
>> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>> Reviewed-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com>
>> ---
>> Revision history:
>> v7 => v8:
>>   - Fix the example in fwnode_get_named_child_node_count() documentation
>>     to use the fwnode_get_named_child_node_count() and not the
>>     device_get_named_child_node_count()
>>   - Fix the rest of the new macro's indentiations
>> v6 => v7:
>>   - Improve kerneldoc
>>   - Inline device_get_named_child_node_count() and change it to call
>>     fwnode_get_named_child_node_count() inside
>>   - Fix indentiation of the new macros
>> v5 => v6:
>>   - Add helpers to also iterate through the nodes.
>> v4 => v5:
>>   - Use given name instead of string 'channel' when counting the nodes
>>   - Add also fwnode_get_child_node_count_named() as suggested by Rob.
>> v3 => v4:
>>   - New patch as suggested by Jonathan, see discussion in:
>> https://lore.kernel.org/lkml/20250223161338.5c896280@jic23-huawei/
>> ---
>>   drivers/base/property.c  | 27 +++++++++++++++++++++++++++
>>   include/linux/property.h | 24 ++++++++++++++++++++++++
>>   2 files changed, 51 insertions(+)
>>
>> diff --git a/drivers/base/property.c b/drivers/base/property.c
>> index c1392743df9c..f42f32ff45fc 100644
>> --- a/drivers/base/property.c
>> +++ b/drivers/base/property.c
>> @@ -945,6 +945,33 @@ unsigned int device_get_child_node_count(const struct device *dev)
>>   }
>>   EXPORT_SYMBOL_GPL(device_get_child_node_count);
>>   
>> +/**
>> + * fwnode_get_named_child_node_count - number of child nodes with given name
>> + * @fwnode: Node which child nodes are counted.
>> + * @name: String to match child node name against.
>> + *
>> + * Scan child nodes and count all the nodes with a specific name. Potential
>> + * 'number' -ending after the 'at sign' for scanned names is ignored.
>> + * E.g.::
>> + *   fwnode_get_named_child_node_count(fwnode, "channel");
>> + * would match all the nodes::
>> + *   channel { }, channel@0 {}, channel@0xabba {}...
>> + *
>> + * Return: the number of child nodes with a matching name for a given device.
>> + */
>> +unsigned int fwnode_get_named_child_node_count(const struct fwnode_handle *fwnode,
>> +					       const char *name)
>> +{
>> +	struct fwnode_handle *child;
>> +	unsigned int count = 0;
>> +
>> +	fwnode_for_each_named_child_node(fwnode, child, name)
>> +		count++;
>> +
>> +	return count;
>> +}
>> +EXPORT_SYMBOL_GPL(fwnode_get_named_child_node_count);
>> +
>>   bool device_dma_supported(const struct device *dev)
>>   {
>>   	return fwnode_call_bool_op(dev_fwnode(dev), device_dma_supported);
>> diff --git a/include/linux/property.h b/include/linux/property.h
>> index e214ecd241eb..a1856e6b714c 100644
>> --- a/include/linux/property.h
>> +++ b/include/linux/property.h
>> @@ -167,10 +167,18 @@ struct fwnode_handle *fwnode_get_next_available_child_node(
>>   	for (child = fwnode_get_next_child_node(fwnode, NULL); child;	\
>>   	     child = fwnode_get_next_child_node(fwnode, child))
>>   
>> +#define fwnode_for_each_named_child_node(fwnode, child, name)		\
>> +	fwnode_for_each_child_node(fwnode, child)			\
>> +		if (!fwnode_name_eq(child, name)) { } else
>> +
>>   #define fwnode_for_each_available_child_node(fwnode, child)		       \
>>   	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_named_child_node(fwnode, child, name)	\
>> +	fwnode_for_each_available_child_node(fwnode, child)		\
>> +		if (!fwnode_name_eq(child, name)) { } else
>> +
> 
> OF only enumerates available nodes via the fwnode API, software nodes don't
> have the concept but on ACPI I guess you could have a difference in nodes
> where you have device sub-nodes that aren't available. Still, these ACPI
> device nodes don't have meaningful names in this context (they're
> 4-character object names) so you wouldn't use them like this anyway.

I believe you have far better understanding on these concepts than I do. 
The reason behind adding fwnode_for_each_available_child_node() was the 
patch 10/10:

-	fwnode_for_each_available_child_node(sensors, node) {
-		if (fwnode_name_eq(node, "sensor")) {
-			if (!thp7312_sensor_parse_dt(thp7312, node))
-				num_sensors++;
-		}
+	fwnode_for_each_available_named_child_node(sensors, node, "sensor") {
+		if (!thp7312_sensor_parse_dt(thp7312, node))
+			num_sensors++;
  	}


> So my question is: is it useful to provide this besides
> fwnode_for_each_named_child_node(), given that both are effectively the
> same?

So, I suppose you're saying the existing thp7312 -driver has no real 
reason to use the 'fwnode_for_each_available_child_node()', but it could 
be using fwnode_for_each_child_node() instead?

If so, I am Ok with dropping the 
'fwnode_for_each_available_named_child_node()' and changing the 10/10 to:

-	fwnode_for_each_available_child_node(sensors, node) {
-		if (fwnode_name_eq(node, "sensor")) {
-			if (!thp7312_sensor_parse_dt(thp7312, node))
-				num_sensors++;
-		}
+	fwnode_for_each_named_child_node(sensors, node, "sensor") {
+		if (!thp7312_sensor_parse_dt(thp7312, node))
+			num_sensors++;
  	}

Do you think that'd be correct?

Yours,
	-- Matti