linux-kernel - Re: [PATCH] usb: host: xhci: Compliance Mode port recovery

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Date:	Tue, 26 Jun 2012 10:51:21 -0700
From:	'Greg KH' <gregkh@...uxfoundation.org>
To:	Alexis Cortes <alexis.cortes@...com>
Cc:	'Sarah Sharp' <sarah.a.sharp@...ux.intel.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	"'Quach, Brian'" <brian.quach@...com>,
	"'Llamas, Jorge'" <jorge.llamas@...com>
Subject: Re: [PATCH] usb: host: xhci: Compliance Mode port recovery

On Tue, Jun 26, 2012 at 12:26:29PM -0500, Alexis Cortes wrote:
> > -----Original Message-----
> > From: Greg KH [mailto:gregkh@...uxfoundation.org]
> > Sent: Friday, June 22, 2012 11:47 AM
> > To: Sarah Sharp
> > Cc: Alexis Cortes; linux-usb@...r.kernel.org;
> linux-kernel@...r.kernel.org;
> > 'Quach, Brian'; 'Llamas, Jorge'
> > Subject: Re: [PATCH] usb: host: xhci: Compliance Mode port recovery
> > 
> > On Fri, Jun 22, 2012 at 09:32:14AM -0700, Sarah Sharp wrote:
> >> This is really going to suck from a power management perspective.
> >> "How do I stop the timer from polling?"  "Oh, you plug a device into
> >> every single port"  "But there's an internal port with nothing
> connected!"
> >> "Uhhh..."
> >>
> >> Greg, are you sure wouldn't consider a sysfs file for changing the
> >> polling interval?
> > 
> > What I really want is a list of the PCI devices that this is affected in,
> > I'm sure that this can be found, as what else would Windows be doing?
> 
> The redriver is completely transparent to the OS and the issue will affect
> all xHCI host controllers.

Ouch.  There's no way to detect by known PCI ids of the devices that you
know have been shipped with this in it?

> > Alexis, what are you going to do about this for Windows?  Why not solve it
> > the same way here for Linux?
> 
> We have implemented a 2 second polling in our Windows XP/Vista/7 xHCI driver
> and are currently engaging with Microsoft to implement a workaround for the
> inbox Win8 driver.

Good luck with that :)

Seriously, 2 seconds isn't that bad, but it can be noticable on some
systems that are in idle mode, as I'm sure you have measured.

greg k-h
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