Re: [RFC PATCH] usb/acpi: Add support usb port power off mechanism for device fixed on the motherboard

[Lan Tianyu <tianyu.lan@intel.com>]

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