linux-kernel - Re: [PATCH] USB: core: Add warm reset while reset-resuming SuperSpeed HUBs

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Date:	Fri, 13 Dec 2013 13:15:52 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Dan Williams <dan.j.williams@...el.com>
cc:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Julius Werner <jwerner@...omium.org>,
	Vikas Sajjan <sajjan.linux@...il.com>,
	Vikas Sajjan <vikas.sajjan@...aro.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	Vincent Palatin <vpalatin@...omium.org>,
	Lan Tianyu <tianyu.lan@...el.com>,
	Ksenia Ragiadakou <burzalodowa@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Vivek Gautam <gautam.vivek@...sung.com>,
	Douglas Anderson <dianders@...omium.org>,
	Felipe Balbi <balbi@...com>, sunil joshi <joshi@...sung.com>
Subject: Re: [PATCH] USB: core: Add warm reset while reset-resuming SuperSpeed
 HUBs

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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