Some plugins have devices with more than one protocol. Logically the protocol
belongs to the device, not the plugin, and in the future we could use this to
further check firmware that's about to be deployed.
This is also not exported into libfwupd (yet?) as it's remains a debug-feature
only -- protocols are not actually required for devices to be added.
Future metadata from the LVFS will set the protocol the firmware is expected to
use. As vendors love to re-use common terms like DFU for incompatible protocols,
namespace them with the controlling company ID with an approximate reverse DNS
namespace.
This also allows more than one plugin to define support for the same protocol,
for instance rts54hid+rts54hub and synapticsmst+dell-dock.
The daemon creates a baseclass of either FuUsbDevice or FuUdevDevice when the
devices are added or coldplugged to match the quirk database and to find out
what plugin to run.
This is proxied to plugins, but they are given the GUsbDevice or GUdevDevice and
the FuDevice is just thrown away. Most plugins either use a FuUsbDevice or
superclassed version like FuNvmeDevice and so we re-create the FuDevice, re-probe
the hardware, re-query the quirk database and then return this to the daemon.
In some cases, plugins actually probe the hardware three times (!) by creating
a FuUsbDevice to get the quirks, so that the plugin knows what kind of
superclass to create, which then itself probes the hardware again.
Passing the temporary FuDevice to the plugins means that the simplest ones can
just fu_plugin_device_add() the passed in object, or create a superclass and
incorporate the actual GUsbDevice and all the GUIDs.
This breaks internal plugin API but speeds up startup substantially and deletes
a lot of code.
