linux-kernel - RE: [PATCH] USB host: Fix lockdep warning in AMD PLL quirk

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Date:	Thu, 7 Apr 2011 17:01:01 +0800
From:	"Xu, Andiry" <Andiry.Xu@....com>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>,
	Alan Stern <stern@...land.harvard.edu>
CC:	Greg Kroah-Hartman <gregkh@...e.de>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<stable@...nel.org>
Subject: RE: [PATCH] USB host: Fix lockdep warning in AMD PLL quirk

> -----Original Message-----
> From: Roedel, Joerg [mailto:Joerg.Roedel@....com]
> Sent: Thursday, April 07, 2011 3:51 PM
> To: Alan Stern
> Cc: Greg Kroah-Hartman; Sarah Sharp; Xu, Andiry;
linux-usb@...r.kernel.org;
> linux-kernel@...r.kernel.org; stable@...nel.org
> Subject: Re: [PATCH] USB host: Fix lockdep warning in AMD PLL quirk
> 
> On Wed, Apr 06, 2011 at 11:16:07AM -0400, Alan Stern wrote:
> > On Wed, 6 Apr 2011, Joerg Roedel wrote:
> 
> > The counter really should be a bool: Has the chipset already been
> > probed or not?  After all, nobody cares how many times this routine
was
> > called.
> >
> > > +	spin_unlock_irqrestore(&amd_lock, flags);
> >
> > This code now contains a bug: You incremented the probe_count
_before_
> > doing the probe.  If another thread calls this routine right now, it
> > will get an incorrect result.
> >
> > Fixing this up should be fairly easy.
> 
> Hmm, we can get rid of the amd_lock completly if every thread uses the
> following call-order:
> 
> 	usb_amd_find_chipset_info();
> 	usb_amd_quirk_pll_enable();
> 	usb_amd_quirk_pll_disable();
> 	usb_amd_dev_put();
> 

The correct order is:

usb_amd_find_chipset_info();
usb_amd_quirk_pll_disable();
usb_amd_quirk_pll_enable();
usb_amd_dev_put();

The pair of pll disable and enable may be called for multiple times.

Thanks,
Andiry

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