Re: use of an intermediate device to handle USB interfaces

[Matthias Drochner <M.Drochner%fz-juelich.de@localhost>]

mouse%Rodents.Montreal.QC.CA@localhost said:
> I recently did an install on a fairly vanilla server system.  I
> counted nine PCI busses in the autoconf output - and at least one
> bridge for each one.  The machine had only one physical PCI bus
> (connectors &c) as far as I could tell. 

My laptop has six of them and not a single PCI slot...
This is PCIexpress where everything is point-to-point.
(This could be made use of for power management, but
the gain of that would arguably be a small increment
compared to eg savings in the CPU.)

> I'm not clear on the
> difference between a device and an interface

A device is basically what plugs into a USB slot,
so eg link and power management is done at this level.
A device logically consists of (one or more) interfaces.
Interfaces often belong to some pre-defined interface
class which can be handled by some class driver.
Thus drivers for common stuff (storage, keyboards, audio...)
attach to some interface.

best regards
Matthias




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