Re: [PATCH] usb: port: add delay after usb_hub_set_port_power()

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Feb 11, 2026 at 10:04:32AM -0500, Alan Stern wrote:
> On Wed, Feb 11, 2026 at 06:36:28PM +0800, Xu Yang wrote:
> > When disable the root hub port, somehow the device is disconnected and
> > re-connected again. This happens because usb_clear_port_feature() does not
> > clear a truly happened port change. That says, in fact, port change event
> > may happen after usb_clear_port_feature() is called. Then the subsequent
> > port change event will have impact on usb device suspend routine.
> 
> This is not a very good description of the problem.  Here's a better 
> one:
> 
> When a port is disabled, an attached device will be disconnected.  This 
> causes a port-status-change event, which will race with hub autosuspend 
> (if the disabled port was the only connected port on its hub), causing 
> an immediate resume and a second autosuspend.  Both of these can be 
> avoided by adding a short delay after the call to 
> usb_hub_set_port_power().

What guarantees that a "short delay" will solve this?  And how long of a
delay?  What guarantees that sleeping will not just reduce the race
window?

thanks,

greg k-h