Re: [RFC PATCH V3 3/3] usb : Add sysfs files to control usb port's power

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

On 2012年06月05日 22:18, Alan Stern wrote:
> On Tue, 5 Jun 2012, Lan Tianyu wrote:
>
>>> The patch does not implement anything at all for "auto".  It should do
>>> _something_.
>>>
>> Yeah, if we don't power off port without device when echo "auto">  portX/control,
>> this patch does nothing about "auto". Original plan is to deal with port without
>> devices firstly. Do you mean I should add the process of port with device in this
>> patch?
>
> At least make a start.  For example, have "auto" turn off the power if
> no device is attached to the port.

In your reply for v2, hint that user space can power off port without
device, so I removed related code. Did I misunderstand?

>> control has three options. "auto", "on" and "off"
>> "auto" - if port without device, power off the port.
>> 	(This patch only cover ports without device)
> Is this option really needed?  Can't userspace check first to see
> whether there is a device, and then write "off" if there isn't?
>
>> 	For ports with device, there is a proposal that if the device was not
>> 	in the suspend at that pointer, the power would remain on but it would
>> 	power off when it was suspended. If the the device was in the suspend,
>> 	"auto" means the device could be put into much lower state so the device
>> 	need to resume and suspend again.
> That makes more sense.  Without this, however, there is no need for
> "auto".
>


>
> If "auto" does nothing, there's no reason to put it in this patch at
> all.  It could be added in a later patch, along with its
> implementation.
OK. I prefer to remove "auto" option in this patch. We can further discuss
the function of "auto".

>
> Alan Stern
>

-- 
Best Regards
Tianyu Lan
linux kernel enabling team
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