But do we need that level of complexity for normal devices usually? In a
normal platform world (SoCs, PV machines) we have a flat memory
can plug our device memory into. We also have a flat IRQ model where we
can plug our device IRQs into.
So the idea for platform devices arose. A platform device is really
device that exposes its qemu_irq slots and memory regions to the world.
That allows us to write machine specific code that maps a platform
wherever the machine thinks fits nicely. It also allows that same
to generate a device tree entry for platform devices easily, as it is
aware of the interrupt lines and places it was mapped to.
A device (read: user) may or may not explictly request to be mapped at a
specific IRQ and/or memory address. If no explicit mapping is requested,
platform devices can get mapped at convenient places by the machine.
The actual pressing issue this solves is that today it's impossible
serial ports from the command line. With this patch set, it's
do so. But it lays the groundwork for much more...