[ltp] T400 does not enter C4/C6 sleep state with USB devices connected

[Richard Neill]

Pedro Ribeiro wrote:
> 
> However, its behaviour is really strange.
> If I plug it in directly into a USB port in the laptop I get this:
> 
> usb 3-1: new low speed USB device using uhci_hcd and address 3
> usb 3-1: New USB device found, idVendor=046d, idProduct=c01d
> usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
> usb 3-1: Product: USB-PS/2 Optical Mouse
> usb 3-1: Manufacturer: Logitech
> 
> 
> But if I plug it in the mini dock, I get this:
> 
> usb 1-5.3: new low speed USB device using ehci_hcd and address 16
> usb 1-5.3: New USB device found, idVendor=046d, idProduct=c01d
> usb 1-5.3: New USB device strings: Mfr=1, Product=2, SerialNumber=0
> usb 1-5.3: Product: USB-PS/2 Optical Mouse
> usb 1-5.3: Manufacturer: Logitech
> 

I suspect what is going on is that the mini-dock contains a USB2 hub. 
This contains a "transaction translator" which sort-of converts USB1 
devices into USB2 devices, as far as the laptop is concerned.

 From the laptop's perspective, the mouse-via-hub is still the same 
device that it was before, but the laptop only has to handle the USB2 
protocol over the bus to the hub. This protocol runs much faster than 
USB1, and has support for power-management.

Richard