On Thu, 2016-02-04 at 14:53 +0800, Peter Chen wrote: > On Wed, Feb 03, 2016 at 11:24:57AM -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@xxxxxxxx> > > > CC: stable@xxxxxxxxxxxxxxx > > > --- > > > 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; > > > > Alan, you may want to skip the first timeout, but quit at the second > timeout, right? If it is, the code may need to change like below: No. If it times out immediately you want a second reset. If it times out any time after that you want a retry of reading the descriptors. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html