linux-kernel - Re: [PATCH] usb: dwc3: be more verbose on ERRATIC

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Date:	Wed, 15 Oct 2014 12:06:10 -0500
From:	Felipe Balbi <balbi@...com>
To:	David Cohen <david.a.cohen@...ux.intel.com>
CC:	Felipe Balbi <balbi@...com>, <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: be more verbose on ERRATIC_ERROR interrupt

On Wed, Oct 15, 2014 at 10:01:45AM -0700, David Cohen wrote:
> On Wed, Oct 15, 2014 at 09:57:18AM -0700, David Cohen wrote:
> > On Wed, Oct 15, 2014 at 12:00:22AM -0500, Felipe Balbi wrote:
> > > Hi,
> > > 
> > > On Tue, Oct 14, 2014 at 01:15:05PM -0700, David Cohen wrote:
> > > > ERRATIC_ERROR interrupt is an event that needs more attention from
> > > > developers than currently implemented, since this indicates a serious
> > > > stability issue. The only way to get warned about it is by selecting the
> > > > maximum driver's verbosity.
> > > > 
> > > > This patch increases a bit the error's verbosity.
> > > > 
> > > > Signed-off-by: David Cohen <david.a.cohen@...ux.intel.com>
> > > > ---
> > > >  drivers/usb/dwc3/gadget.c | 3 ++-
> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > > > index 3818b26bfc05..132e761d62e4 100644
> > > > --- a/drivers/usb/dwc3/gadget.c
> > > > +++ b/drivers/usb/dwc3/gadget.c
> > > > @@ -2484,7 +2484,8 @@ static void dwc3_gadget_interrupt(struct dwc3 *dwc,
> > > >  		dev_vdbg(dwc->dev, "Start of Periodic Frame\n");
> > > >  		break;
> > > >  	case DWC3_DEVICE_EVENT_ERRATIC_ERROR:
> > > > -		dev_vdbg(dwc->dev, "Erratic Error\n");
> > > > +		WARN_ON_ONCE(1);
> > > > +		dev_dbg(dwc->dev, "Erratic Error\n");
> > > 
> > > how about:
> > > 		WARN_ONCE(true, "Erratic Error\n");
> > > 
> > > instead ?
> > 
> > When erratic error event happens, in my experience it is usually
> > followed but many of them in a row. It may end up too verbose.
> 
> Oops, sorry for my confusion. I read WARN(), not WARN_ONCE() when I read
> for the first time :)
> 
> I let the dev_dbg() because it may be useful to get all the occurrences
> in case debug is enabled. But WARN_ONCE() is fine too if you prefer.

We might WARN_ONCE() and forcibly disconnect from host as the platform
worn't work anymore after Erratic Error happens. Then just make that
clear with "Erratic Error: disconnecting from host\n" or something like
that.

The only way to fix erratic error (by fixing code - probably PHY driver)
will require rebooting the platform anyway. At a minimum, you'd have to
unload and reload dwc3.ko, just make sure (if you can reproduce erratic
error easily) modprobe -r dwc3 && modprobe dwc3 still causes dwc3 to
reconnect to host.

cheers

-- 
balbi

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