[PATCH v5 01/23] driver core: Add pre_probe callback to bus_type

[Alan Stern]

On Thu, 17 Sep 2015, Tomeu Vizoso wrote:

> Some buses (eg. AMBA) need access to some HW resources (it may need a
> clock to be enabled so a device ID can be read) before a device can be
> matched to a driver.
> 
> The pre_probe callback allows the device-driver core to request the bus
> to perform this initialization and can defer the probe if any of the
> resources needed are missing.
> 
> This gives us more flexibility when setting the order in which devices
> are probed because the resources needed to get the matching information
> don't need to be available by the time that the bus devices are
> registered.

Can't the subsystem do this itself in its matching routine?

Alan Stern