[ltp] T400 does not enter C4/C6 sleep state with USB devices
Henrique de Moraes Holschuh
Mon, 22 Feb 2010 21:25:02 -0300
On Mon, 22 Feb 2010, Pedro Ribeiro wrote:
> >> 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?
> You are right, this only happens with USB 1.1 devices! The only USB1
> device I have is my logitech mouse.
UHCI is a utter piece of crap...
> 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
> So if I plug it in the dock, I get C4/C6 state on AC/battery and it
> uses ehci-hcd.
USB 1.1 in a USB2.0 hub connected to a USB2.0 root port :-)
You can use the same trick to get your USB1.1 mouse to work under EHCI, I
suppose. Find a *good* USB 2.0 hub, and have it between your mouse and the
laptop... that might do it.
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