Man page 9 : devm_input_allocate_device

devm_input_allocate_device - allocate managed input device

struct input_dev * devm_input_allocate_device(struct device *  dev );

dev
    device owning the input device being created

Returns prepared struct input_dev or NULL.

Managed input devices do not need to be explicitly unregistered or freed as it will be done automatically when owner device unbinds from its driver (or binding fails). Once managed input device is allocated, it is ready to be set up and registered in the same fashion as regular input device. There are no special devm_input_device_[un]register variants, regular ones work with both managed and unmanaged devices, should you need them. In most cases however, managed input device need not be explicitly unregistered or freed.

the owner device is set up as parent of input device and users should not override it.