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8ebe023800
On rk3288-veyron devices on Chrome OS it was found that plugging in an
Arduino-based USB device could cause the system to lockup, especially
if the CPU Frequency was at one of the slower operating points (like
100 MHz / 200 MHz).
Upon tracing, I found that the following was happening:
* The USB device (full speed) was connected to a high speed hub and
then to the rk3288. Thus, we were dealing with split transactions,
which is all handled in software on dwc2.
* Userspace was initiating a BULK IN transfer
* When we sent the SSPLIT (to start the split transaction), we got an
ACK. Good. Then we issued the CSPLIT.
* When we sent the CSPLIT, we got back a NAK. We immediately (from
the interrupt handler) started to retry and sent another SSPLIT.
* The device kept NAKing our CSPLIT, so we kept ping-ponging between
sending a SSPLIT and a CSPLIT, each time sending from the interrupt
handler.
* The handling of the interrupts was (because of the low CPU speed and
the inefficiency of the dwc2 interrupt handler) was actually taking
_longer_ than it took the other side to send the ACK/NAK. Thus we
were _always_ in the USB interrupt routine.
* The fact that USB interrupts were always going off was preventing
other things from happening in the system. This included preventing
the system from being able to transition to a higher CPU frequency.
As I understand it, there is no requirement to retry super quickly
after a NAK, we just have to retry sometime in the future. Thus one
solution to the above is to just add a delay between getting a NAK and
retrying the transmission. If this delay is sufficiently long to get
out of the interrupt routine then the rest of the system will be able
to make forward progress. Even a 25 us delay would probably be
enough, but we'll be extra conservative and try to delay 1 ms (the
exact amount depends on HZ and the accuracy of the jiffy and how close
the current jiffy is to ticking, but could be as much as 20 ms or as
little as 1 ms).
Presumably adding a delay like this could impact the USB throughput,
so we only add the delay with repeated NAKs.
NOTE: Upon further testing of a pl2303 serial adapter, I found that
this fix may help with problems there. Specifically I found that the
pl2303 serial adapters tend to respond with a NAK when they have
nothing to say and thus we end with this same sequence.
Change-Id: Ie9306eeef2694ceb59a07658905223f698b74e9a
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: William Wu <william.wu@rock-chips.com>
(cherry picked from git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git next
commit 38d2b5fb75)
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.