linux-kernel - Re: [PATCH] usb: host: xhci-plat: Enable XHCI_SPURIOUS

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Date:	Sun, 30 Jun 2013 14:00:28 -0700
From:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
To:	George Cherian <george.cherian@...com>
Cc:	linux-usb@...r.kernel.org, balbi@...com,
	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org
Subject: Re: [PATCH] usb: host: xhci-plat: Enable XHCI_SPURIOUS_SUCCESS quirk
 for xhci-plat

On Wed, Jun 26, 2013 at 09:53:34AM -0700, Sarah Sharp wrote:
> On Wed, Jun 26, 2013 at 02:28:57PM +0530, George Cherian wrote:
> > Synopsis xhci controllers with hci_version > 0.96 gives spurious success
> > events on short packet completion. During webcam capture the
> > "ERROR Transfer event TRB DMA ptr not part of current TD" was observed.
> > The same application works fine with synopsis controllers hci_version 0.96.
> 
> It's a known issue.  The xHCI 1.0 spec changed how hardware handles
> short packets.  The HW will notify SW of the TRB where the short packet,
> and it will also give a successful status for the last TRB in a TD (the
> one with the IOC flag set).  On the second successful status, that
> warning will be triggered in the driver.
> 
> Software is now supposed to not assume the TD as done until it gets that
> last successful status.  That means we have a slight race condition,
> although it should have little practical impact.  This patch papers over
> that issue.
> 
> I will take this patch, but will add the note that is on my long-term
> to-do list to fix this issue.

Actually, since it applies to both xhci-plat and xhci-pci hosts, can you
move setting this quirk into xhci_gen_setup?

Sarah Sharp

> > Signed-off-by: George Cherian <george.cherian@...com>
> > ---
> >  drivers/usb/host/xhci-plat.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> > index 93ad67e..e63c6d3 100644
> > --- a/drivers/usb/host/xhci-plat.c
> > +++ b/drivers/usb/host/xhci-plat.c
> > @@ -25,6 +25,16 @@ static void xhci_plat_quirks(struct device *dev, struct xhci_hcd *xhci)
> >  	 * dev struct in order to setup MSI
> >  	 */
> >  	xhci->quirks |= XHCI_BROKEN_MSI;
> > +
> > +	/*
> > +	 * In some xhci controllers which follows xhci 1.0 spec gives a spurious
> > +	 * success event after a short transfer. This quirk will ignore such
> > +	 * spurious event. Hit this issue in synopsis xhci controllers with
> > +	 * hci_version > 0.96
> > +	 */
> > +
> > +	if (xhci->hci_version > 0x96)
> > +		xhci->quirks |= XHCI_SPURIOUS_SUCCESS;
> >  }
> >  
> >  /* called during probe() after chip reset completes */
> > -- 
> > 1.8.1.4
> > 
> --
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