On 2013/3/29 4:47, Sarah Sharp wrote:
On Thu, Mar 28, 2013 at 07:58:47AM +0800, Lan Tianyu wrote:
On 2013/3/28 2:47, Alan Stern wrote:
On Thu, 28 Mar 2013, Lan Tianyu wrote
What happens if there's no device plugged in to the port, but the hub
is enabled for remote wakeup? How will the hub be able to detect a
plug-in event if the port isn't powered?
Alan Stern
Hi Alan:
Great thanks for your review.
The hub will not detect the new devices. From my opinion, this
depends on the user space since the port only will be powered off when
pm qos NO_POWER_OFF flag is unset(it is default to be set). If unset
the flag, losing plug-in event should have been took into account.
So basically, you're saying that any new distro policy that turns off
port power will need to re-enable it if the user wants hotplug events
from a hub? I think that's a very important thing to document.
I really think we need to add more description about the port power off
mechanisms to Documentation/usb/power-management.txt. There's a little
bit in Documentation/ABI/testing/sysfs-bus-usb, but since this mechanism
is so new, I think we need to educate distro users on its effects and
suggestions on how to use it. Can you take a first stab at an overview,
and I'll let you know what's missing?
That's good idea. Ok. I will do that.
Sarah Sharp
--
Best Regards
Tianyu Lan
linux kernel enabling team
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