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

[Pedro Ribeiro]

On 18 February 2010 18:36, Henrique de Moraes Holschuh <hmh@hmh.eng.br> wro=
te:
> On Thu, 18 Feb 2010, Pedro Ribeiro wrote:
>> I spent lots of hours trying to figure out why my T400 would not enter
>> C4 and C6 sleep states.
>>
>> Here are my findings for anyone which is interested:
>> - When a USB device is connected, even if it supports USB autosuspend,
>> the cpu will never go down more than C3 (apparently the mode is
>> disabled by the BIOS).
>> - After removing all the USB devices, in AC it enters C4 and in
>> battery it enters C6.
>>
>> So one more reason not to use USB devices while on battery...
>
> Did you try that using only EHCI (unload uhci_hcd) and USB2.0 devices?
>
> --
> =A0"One disk to rule them all, One disk to find them. One disk to bring
> =A0them all and in the darkness grind them. In the Land of Redmond
> =A0where the shadows lie." -- The Silicon Valley Tarot
> =A0Henrique Holschuh
>

You are right, this only happens with USB 1.1 devices! The only USB1
device I have is my logitech mouse.

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=3D046d, idProduct=3Dc01d
usb 3-1: New USB device strings: Mfr=3D1, Product=3D2, SerialNumber=3D0
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=3D046d, idProduct=3Dc01d
usb 1-5.3: New USB device strings: Mfr=3D1, Product=3D2, SerialNumber=3D0
usb 1-5.3: Product: USB-PS/2 Optical Mouse
usb 1-5.3: Manufacturer: Logitech


So if I plug it in the dock, I get C4/C6 state on AC/battery and it
uses ehci-hcd.

But if I plug it directly on the laptop in any usb plug, I don't get
more than C3 state and it uses uhci-hcd.

If I remove the uhci-hcd module when the mouse is plugged directly to
the laptop, it stops working.

Is this some sort of bug or is it normal?

Many thanks,
Pedro