Hi,
USB devices can support both 1.1 and 2.0, right? Who decides which
protocol is used then? I think the OS can speak 1.1 to the device even
in case a ehci controller is present (but unused by the OS), right?
AFAIK the OS must tell the EHCI that it should hand the device off to
the UHCI/OHCI companion before it can use it there.
Huh? Compatibility-wise it makes sense to do it the other way around
(i.e. have it @ UHCI/OHCI by default and move to EHCI on request), so a
OS which knows nothing about EHCI can cope.
If they should be accessed via the EHCI or a companion controller
depends on what the OS requests. And USB 2.0 says that any device that
supports High Speed must also support Full Speed and therefore be
accessible using the companion (at least that's what I understand).
Hmm, ok, so no shortcut even for emulated devices. Not that it would
have helped much as we have to cover host devices anyway.
Also I think one ehci controller can have multiple uhci companion
controllers. At least lspci on my T60 suggests that:
00:1d.0 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI
Controller #1 (rev 02)
00:1d.1 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI
Controller #2 (rev 02)
00:1d.2 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI
Controller #3 (rev 02)
00:1d.3 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI
Controller #4 (rev 02)
00:1d.7 USB Controller: Intel Corporation 82801G (ICH7 Family) USB2 EHCI
Controller (rev 02)
cheers,
Gerd
