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When the xHCI driver attempts to cancel a transfer, it issues a Stop Endpoint command and waits for the host controller to indicate which TRB it was in the middle of processing. The host will put an event TRB with completion code COMP_STOP on the event ring if it stops on a control transfer TRB (or other types of transfer TRBs). The ring handling code is supposed to set ep->stopped_trb to the TRB that the host stopped on when this happens. Unfortunately, there is a long-standing bug in the control transfer completion code. It doesn't actually check to see if COMP_STOP is set before attempting to process the transfer based on which part of the control TD completed. So when we get an event on the data phase of the control TRB with COMP_STOP set, it thinks it's a normal completion of the transfer and doesn't set ep->stopped_td or ep->stopped_trb. When the ring handling code goes on to process the completion of the Stop Endpoint command, it sees that ep->stopped_trb is not a part of the TD it's trying to cancel. It thinks the hardware has its enqueue pointer somewhere further up in the ring, and thinks it's safe to turn the control TRBs into no-op TRBs. Since the hardware was in the middle of the control TRBs to be cancelled, the proper software behavior is to issue a Set TR dequeue pointer command. It turns out that the NEC host controllers can handle active TRBs being set to no-op TRBs after a stop endpoint command, but other host controllers have issues with this out-of-spec software behavior. Fix this behavior. This patch should be backported to kernels as far back as 2.6.31, but it may be a bit challenging, since process_ctrl_td() was introduced in some refactoring done in 2.6.36, and some endian-safe patches added in 2.6.40 that touch the same lines. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com> Cc: stable@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 ("khubd").
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.