On 2012/5/12 2:12, Sarah Sharp wrote:
On Fri, May 11, 2012 at 01:44:26PM -0400, Alan Stern wrote:
On Sat, 12 May 2012, Lan Tianyu wrote:
The power saving depends on devices. I test a usb3.0 ssd. The power saving of
power off is about 2.2w more than just selective suspend. In theory, power
off can help to save remaining power after selective suspend.
That's a lot of power! Suspended USB devices aren't supposed to
consume more than 2.5 mA of bus current, which at 5 V amounts to<=
0.0125 W. Does the port really use that much? Or does the SSD have a
separate power supply that it disables when port power is removed?
I actually suspect that the host controller is powering off several PLLs
if all the ports are powered off. After all, if it doesn't have to pay
attention to connects, disconnects, or remote wakeup, it can power off a
lot more circuitry, and possibly even enter D3cold instead of D3hot when
the PCI device is suspended (depending on what board Tianyu is testing
on). But I agree that it would be interesting to see if the SSD has a
separate power supply that it's turning off.
There is no a separate power supply. All power came from host desktop
via usb cable.
--
Best Regards
Tianyu Lan
linux kernel enabling team
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