Re: [PATCH] USB: core: Add warm reset while reset-resuming SuperSpeedHUBs

[Alan Stern]

On Fri, 13 Dec 2013, Dan Williams wrote:

> > I'm actually leaning towards enabling the check for warm reset broadly.
> > It seems like it wouldn't hurt to issue a warm reset on the USB 3.0
> > ports if they're in compliance, poll, or rx.detect.  So, let's enable
> > this broadly in xhci_resume, mark the patch for stable, but ask for the
> > backport to be delayed until 3.13.3 is out, to allow for more testing.
> > If anyone complains of xHCI behavior changes, we'll change the code to
> > add a quirk.
> 
> Is there a clean way to make this per-port rather than globally at
> xhci_resume()?  I am looking to hook into this for port power recovery
> as Tianyu's testing encountered "warm reset required" conditions at
> runtime_resume.  I'm still on the hunt for a solid reproducer, but it
> indicates this is a more general quirk with power session recovery.

There's no reason you can't do per-port testing inside xhci_resume
(assuming you know what to test for) as well as putting a warm reset in
the port-power handler of xhci_hub_control.

Of course, doing simultaneous warm resets on multiple ports will use 
less time than resetting each port individually, in sequence.

Alan Stern

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