On Wed, May 29, 2024 at 05:24:03PM +0300, Andy Shevchenko wrote: > On Wed, May 29, 2024 at 12:48 PM Laurent Pinchart wrote: > > On Wed, May 29, 2024 at 09:16:43AM +0300, Andy Shevchenko wrote: > > > On Tue, May 28, 2024 at 11:20 PM Laurent Pinchart wrote: > > > > On Tue, May 28, 2024 at 10:36:06PM +0300, Andy Shevchenko wrote: > > ... > > > > > > > + device_set_of_node_from_dev(dev, dev->parent); > > > > > > > > > > Why not device_set_node()? > > > > > > > > Because device_set_of_node_from_dev() is meant for this exact use case, > > > > where the same node is used for multiple devices. It also puts any > > > > previous dev->of_node, ensuring proper refcounting when devices are > > > > unbound and rebound, without being deleted. > > > > > > When will the refcount be dropped (in case of removal of this device)? > > > Or you mean it shouldn't? > > > > Any refcount taken on the OF node needs to be dropped. The device core > > only drops the refcount when the device is being deleted, not when > > there's an unbind-rebind cycle without deletion of the device (as > > happens for instance when the module is unloaded and reloaded). > > Under "device" you meant the real hardware, as Linux device (instance > of the struct device object) is being rebuilt AFAIK)? I mean struct device. The driver core will drop the reference in platform_device_release(), called when the last reference to the platform device is released, just before freeing the platform_device instance. This happens after the device is removed from the system (e.g. hot-unplug), but not when a device is unbound from a driver and rebound (e.g. module unload and reload). > > This has > > to be handled by the driver. device_set_of_node_from_dev() handles it. > > But why do you need to keep a parent node reference bumped? > Only very few drivers in the kernel use this API and I believe either > nobody knows what they are doing and you are right, or you are doing > something which is not needed. I need to set the of_node and fwnode fields of struct device to enable OF-based lookups of GPIOs and PWMs. The of_node field is meant to be populated by the driver core when the device is created, with a reference to the OF node. When populated directly by driver, this needs to be taken into account, and drivers need to ensure the reference will be released correctly. device_set_of_node_from_dev() is meant for that. -- Regards, Laurent Pinchart
