On Fri, Jul 18, 2014 at 04:25:23PM -0400, Alan Stern wrote: > Some OHCI controllers (most notably those made by NVIDIA, but others > too) sometimes lose track of completed Transfer Descriptors. When a TD > completes, the controller is supposed to add it to the start of the > Done Queue, to let the driver know the transfer is finished. The buggy > controllers occasionally fail to do this. > > ohci-hcd already contains a couple of ad-hoc mechanisms for dealing > with these failures. One of the quirk handlers (for Compaq ZF Micro) > looks for lost TDs on an interrupt endpoint. In addition, the driver > recognizes that whenever a TD is on the Done Queue, all the earlier TDs > for the same endpoint must have completed as well, even if they aren't > on the Done Queue. > > Still, these mechanisms don't handle all the possible scenarios. Lost > TDs have been observed for non-interrupt endpoints, and if the lost TD > is the last one in a transfer then there might not be anything > following it in the Done Queue. > > This patch series replaces the ad-hoc mechanisms with a general > approach. A new I/O watchdog routine runs every 200 ms as long as > there are any active URBs. The routine scans the lists of TDs, looking > for any which have completed but haven't shown up in the Done Queue, > and takes care of them. (This will add a small amount of overhead, but > OHCI has never been high-throughput.) The routine also checks for > controllers malfunctioning so badly that they are unusable, and > declares them dead. > > Making these changes requires a certain amount of care, because the > controller might add a TD to the Done Queue any time up to a > millisecond after the TD completes. The watchdog routine has to make > sure it doesn't race with the hardware, and the done list (the driver's > equivalent of the hardware's Done Queue) has to be treated differently > from the way it is now. Also, there will be two pathways by which URBs > may complete: the hardware IRQ handler and the watchdog routine. This > requires the driver to make sure that URB completions are always > single-threaded. > > The first four patches in this series remove the ad-hoc zfmicro quirk > and make other preliminary adjustments. The last two patches add the > I/O watchdog and add to it a check for a non-updating frame counter > (another type of hardware problem observed in the field). > > In the past, users have reported controller failures like these that > ended up hanging the kernel's USB stack. With these changes in place, > the hardware problems will show up as graceful failures, leaving the > rest of the USB subsystem intact. Very nice work, the things drivers have to do to work around broken hardware... All now applied, thanks. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
