On Mon, Sep 24, 2012 at 01:05:08PM -0700, Sarah Sharp wrote: > On Mon, Sep 24, 2012 at 03:50:04PM -0400, Alan Stern wrote: > > On Mon, 24 Sep 2012, Sarah Sharp wrote: > > > > > When a device with an isochronous endpoint is behind a hub plugged into > > > the Intel Panther Point xHCI host controller, and the driver submits > > > multiple frames per URB, the xHCI driver will set the Block Event > > > Interrupt (BEI) flag on all but the last TD for the URB. This causes > > > the host controller to place an event on the event ring, but not send an > > > interrupt. When the last TD for the URB completes, BEI is cleared, and > > > we get an interrupt for the whole URB. > > > > > > However, under a Panther Point xHCI host controller, if the parent hub > > > is unplugged when one or more events from transfers with BEI set are on > > > the event ring, a port status change event is placed on the event ring, > > > but no interrupt is generated. This means URBs stop completing, and the > > > USB device disconnect is not noticed. Something like a USB headset will > > > cause mplayer to hang when the device is disconnected. > > > > Won't that also cause a problem for hot-unplug detection? How will the > > hub driver learn about the unplug event if there's no interrupt? > > There will be an interrupt if we don't use the BEI flag. That's what > this patch fixes. > > The BEI flag is only supposed to block isochronous interrupts, and only > if there was no error associated with the transfer. But the Panther > Point xHCI host is broken, and the BEI flag stops unrelated interrupts, > like the port status change event interrupt. > > > Also, does this same problem affect bulk transfers, in particular those > > using scatter-gather? > > Bulk transfers, including scatter-gather transfers, are always > translated into one TD, and the BEI flag is not used. AFAIK, this bug > only affects transfers with the BEI flag set, so bulk transfers should > be fine. Alan, any more questions on this patch? I'd like to get it (and a couple other bug fixes) pushed to Greg this week before the 3.7 merge window. Sarah Sharp -- 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
