[Bug 60824] [PATCH][regression] Cambridge Silicon Radio, Ltd Bluetooth Dongle unusable

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=60824

--- Comment #167 from Hans de Goede (jwrdegoede@fedoraproject.org) ---
mirh, hi, interesting comment.

I wonder if this perhaps is a USB packet timing issue, rather then a signal
strength issue, esp. the " "hci0: unexpected event for opcode 0x0000" error
that I'm only getting..." bit makes me wonder this.

Your old PC was likely using an EHCI controller. Where as your new PC is using
a xHCI controller, or a mix of EHCI + xHCI.  There is a subtle problem with
USB1/2 compatibility and xHCI controllers. the UHCI/EHCI USB1/2 controllers
have a frameclock of 1 ms and when sending a new USB packet to a device just
after the frame clock-tick, it will get delayed until the next frame. The xHCI
controller however will send any new USB control/bulk transfers *immediately*
if there is room for it on the BUs schedule (IOW if the bus is otherwise idle).

I've recently helped fix support for some old USB scanners by inserting a 1 ms
delay for some requests during the initialization of the scanner since the new
xHCI behavior made the time between 2 requests too short for the firmware of
the scanner to handle.  I wonder if something similar is going on here.

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