Re: [PATCH net-next 1/3] device property: Introduce fwnode_for_each_available_child_node_scoped()

[Javier Carrasco <javier.carrasco.cruz@gmail.com>]

On 11/10/2024 11:54, Sakari Ailus wrote:
> 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@gmail.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.
> 

fwnode_device_is_available() is indeed called in
fwnode_get_next_available_child_node(), as I stated a couple of lines below.

My question on the other hand was how that is called in
fwnode_for_each_child_node(), as I could not see any call to check
availability in acpi_get_next_subnode().
That is what confused me about the _available_ macros being the same as
their counterparts without the _available_.

Could you please clarify that? Thanks again.

>>
>> 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?
>