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由 Benjamin Tisssoires 提交于
This fix (not very clean though) should fix the long time USB3 issue that was spotted last year. The rational has been given by Hans de Goede: ---- I think the most likely cause for this is a firmware bug in the unifying receiver, likely a race condition. The most prominent difference between having a USB-2 device plugged into an EHCI (so USB-2 only) port versus an XHCI port will be inter packet timing. Specifically if you send packets (ie hid reports) one at a time, then with the EHCI controller their will be a significant pause between them, where with XHCI they will be very close together in time. The reason for this is the difference in EHCI / XHCI controller OS <-> driver interfaces. For non periodic endpoints (control, bulk) the EHCI uses a circular linked-list of commands in dma-memory, which it follows to execute commands, if the list is empty, it will go into an idle state and re-check periodically. The XHCI uses a ring of commands per endpoint, and if the OS places anything new on the ring it will do an ioport write, waking up the XHCI making it send the new packet immediately. For periodic transfers (isoc, interrupt) the delay between packets when sending one at a time (rather then queuing them up) will be even larger, because they need to be inserted into the EHCI schedule 2 ms in the future so the OS driver can be sure that the EHCI driver does not try to start executing the time slot in question before the insertion has completed. So a possible fix may be to insert a delay between packets being send to the receiver. ---- I tested this on a buggy Haswell USB 3.0 motherboard, and I always get the notification after adding the msleep. Signed-off-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com> Signed-off-by: NJiri Kosina <jkosina@suse.cz>
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