Re: [PATCH] usb: retry reset if a device times out

[Oliver Neukum <oneukum@suse.com>]

On Wed, 2016-02-03 at 11:24 -0500, Alan Stern wrote:
> On Wed, 3 Feb 2016, Oliver Neukum wrote:
> 
> > Some devices I got show an inability to operate right after
> > power on if they are already connected. They are beyond recovery
> > if the descriptors are requested multiple times. So in case of
> > a timeout we rather bail early and reset again.
> > 
> > This patch is a rework of a patch that fell through the cracks.
> > http://www.spinics.net/lists/linux-usb/msg103263.html
> > 
> > Signed-off-by: Oliver Neukum <oneukum@suse.com>
> > CC: stable@vger.kernel.org
> > ---
> >  drivers/usb/core/hub.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index f912fe6..2124c4e 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -4496,7 +4496,12 @@ hub_port_init(struct usb_hub *hub, struct usb_device *udev, int port1,
> >  						r = -EPROTO;
> >  					break;
> >  				}
> > -				if (r == 0)
> > +				/*
> > +				 * Some devices time out if they are powered on
> > +				 * when already connected. They need a second
> > +				 * reset.
> > +				 */
> > +				if (r == 0  || r == -ETIMEDOUT)
> >  					break;
> >  			}
> >  			udev->descriptor.bMaxPacketSize0 =
> > 
> 
> Hmmm.  Your device fails completely if there are multiple attempts 
> without a reset in between, right?
> 
> What about devices which always time out the first control request
> after a reset?  I can't be certain any such devices exist, but it
> wouldn't be surprising given the range of hardware bugs in USB devices.
> 
> Would it be safer to do this instead?
> 
> 				if (r == 0 || (r == -ETIMEDOUT &&
> 						j = 0))
> 					break;
Indeed. Greg, I'll make an improved patch.

	Regards
		Oliver