On Wed, May 29, 2024 at 5:35 PM Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > 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 is something I need to refresh in my memory. Any pointers (the links to the exact code lines are also okay) where I can find the proof of what you are saying. (It's not that I untrust you, it's just that I take my time on studying it.) > > > 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 s/very/a/ (sorry for the confusion) > > 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. What you are doing is sharing the parent node with the child, but at the same time you bump the parent's reference count. As this is a child of MFD I don't think you need this as MFD already takes care of it via parent -> child natural dependencies. Is it incorrect understanding? -- With Best Regards, Andy Shevchenko
