From 42c22dbf81ebd1146960875ddfe71630cb2b3ae6 Mon Sep 17 00:00:00 2001 From: Benjamin Tisssoires Date: Wed, 8 Jan 2014 17:18:45 -0500 Subject: [PATCH] HID: logitech-dj: Fix USB 3.0 issue 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: Benjamin Tissoires Signed-off-by: Jiri Kosina --- drivers/hid/hid-logitech-dj.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/hid/hid-logitech-dj.c b/drivers/hid/hid-logitech-dj.c index a7947d8251a8..f45279c3b11a 100644 --- a/drivers/hid/hid-logitech-dj.c +++ b/drivers/hid/hid-logitech-dj.c @@ -516,6 +516,14 @@ static int logi_dj_recv_switch_to_dj_mode(struct dj_receiver_dev *djrcv_dev, dj_report->report_params[CMD_SWITCH_PARAM_TIMEOUT_SECONDS] = (u8)timeout; retval = logi_dj_recv_send_report(djrcv_dev, dj_report); kfree(dj_report); + + /* + * Ugly sleep to work around a USB 3.0 bug when the receiver is still + * processing the "switch-to-dj" command while we send an other command. + * 50 msec should gives enough time to the receiver to be ready. + */ + msleep(50); + return retval; } -- 2.20.1