d82a810eed
I find that when I plug a full speed (NOT high speed) hub into a dwc2
port and then I plug a bunch of devices into that full speed hub that
dwc2 goes bat guano crazy. Specifically, it just spews errors like this
in the console:
usb usb1: clear tt 1 (9043) error -22
The specific test case I used looks like this:
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=dwc2/1p, 480M
|__ Port 1: Dev 17, If 0, Class=Hub, Driver=hub/4p, 12M
|__ Port 2: Dev 19, If 0, ..., Driver=usbhid, 1.5M
|__ Port 4: Dev 20, If 0, ..., Driver=usbhid, 12M
|__ Port 4: Dev 20, If 1, ..., Driver=usbhid, 12M
|__ Port 4: Dev 20, If 2, ..., Driver=usbhid, 12M
Showing VID/PID:
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 017: ID 03eb:3301 Atmel Corp. at43301 4-Port Hub
Bus 001 Device 020: ID 045e:0745 Microsoft Corp. Nano Transceiver ...
Bus 001 Device 019: ID 046d:c404 Logitech, Inc. TrackMan Wheel
I spent a bunch of time trying to figure out why there are errors to
begin with. I believe that the issue may be a hardware issue where the
transceiver sometimes accidentally sends a PREAMBLE packet if you send a
packet to a full speed device right after one to a low speed device.
Luckily the USB driver retries and the second time things work OK.
In any case, things kinda seem work despite the errors, except for the
"clear tt" spew mucking up my console. Chalk it up for a win for
retries and robust protocols.
So getting back to the "clear tt" problem, it appears that we get those
because there's not actually a TT here to clear. It's my understanding
that when dwc2 operates in low speed or full speed mode that there's no
real TT out there. That makes all these attempts to "clear the TT"
somewhat meaningless and also causes the spew in the log.
Let's just skip all the useless TT clears. Eventually we should root
cause the errors, but even if we do this is still a proper fix and is
likely to avoid the "clear tt" error in the future.
Note that hooking up a Full Speed USB Audio Device (Jabra 510) to this
same hub with the keyboard / trackball shows that even audio works over
this janky connection. As a point to note, this particular change (skip
bogus TT clears) compared to just commenting out the dev_err() in
hub_tt_work() actually produces better audio.
Note: don't ask me where I got a full speed USB hub or whether the
massive amount of dust that accumulated on it while it was in my junk
box affected its funtionality. Just smile and nod.
Acked-by: John Youn <johnyoun@synopsys.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
To understand all the Linux-USB framework, you'll use these resources:
* This source code. This is necessarily an evolving work, and
includes kerneldoc that should help you get a current overview.
("make pdfdocs", and then look at "usb.pdf" for host side and
"gadget.pdf" for peripheral side.) Also, Documentation/usb has
more information.
* The USB 2.0 specification (from www.usb.org), with supplements
such as those for USB OTG and the various device classes.
The USB specification has a good overview chapter, and USB
peripherals conform to the widely known "Chapter 9".
* Chip specifications for USB controllers. Examples include
host controllers (on PCs, servers, and more); peripheral
controllers (in devices with Linux firmware, like printers or
cell phones); and hard-wired peripherals like Ethernet adapters.
* Specifications for other protocols implemented by USB peripheral
functions. Some are vendor-specific; others are vendor-neutral
but just standardized outside of the www.usb.org team.
Here is a list of what each subdirectory here is, and what is contained in
them.
core/ - This is for the core USB host code, including the
usbfs files and the hub class driver ("hub_wq").
host/ - This is for USB host controller drivers. This
includes UHCI, OHCI, EHCI, and others that might
be used with more specialized "embedded" systems.
gadget/ - This is for USB peripheral controller drivers and
the various gadget drivers which talk to them.
Individual USB driver directories. A new driver should be added to the
first subdirectory in the list below that it fits into.
image/ - This is for still image drivers, like scanners or
digital cameras.
../input/ - This is for any driver that uses the input subsystem,
like keyboard, mice, touchscreens, tablets, etc.
../media/ - This is for multimedia drivers, like video cameras,
radios, and any other drivers that talk to the v4l
subsystem.
../net/ - This is for network drivers.
serial/ - This is for USB to serial drivers.
storage/ - This is for USB mass-storage drivers.
class/ - This is for all USB device drivers that do not fit
into any of the above categories, and work for a range
of USB Class specified devices.
misc/ - This is for all USB device drivers that do not fit
into any of the above categories.