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In order to giveback a canceled URB, we must ensure that the xHCI hardware will not access the buffer in an URB. We can't modify the buffer pointers on endpoint rings without issuing and waiting for a stop endpoint command. Since URBs can be canceled in interrupt context, we can't wait on that command. The old code trusted that the host controller would respond to the command, and would giveback the URBs in the event handler. If the hardware never responds to the stop endpoint command, the URBs will never be completed, and we might hang the USB subsystem. Implement a watchdog timer that is spawned whenever a stop endpoint command is queued. If a stop endpoint command event is found on the event ring during an interrupt, we need to stop the watchdog timer with del_timer(). Since del_timer() can fail if the timer is running and waiting on the xHCI lock, we need a way to signal to the timer that everything is fine and it should exit. If we simply clear EP_HALT_PENDING, a new stop endpoint command could sneak in and set it before the watchdog timer can grab the lock. Instead we use a combination of the EP_HALT_PENDING flag and a counter for the number of pending stop endpoint commands (xhci_virt_ep->stop_cmds_pending). If we need to cancel the watchdog timer and del_timer() succeeds, we decrement the number of pending stop endpoint commands. If del_timer() fails, we leave the number of pending stop endpoint commands alone. In either case, we clear the EP_HALT_PENDING flag. The timer will decrement the number of pending stop endpoint commands once it obtains the lock. If the timer is the tail end of the last stop endpoint command (xhci_virt_ep->stop_cmds_pending == 0), and the endpoint's command is still pending (EP_HALT_PENDING is set), we assume the host is dying. The watchdog timer will set XHCI_STATE_DYING, try to halt the xHCI host, and give back all pending URBs. Various other places in the driver need to check whether the xHCI host is dying. If the interrupt handler ever notices, it should immediately stop processing events. The URB enqueue function should also return -ESHUTDOWN. The URB dequeue function should simply return the value of usb_hcd_check_unlink_urb() and the watchdog timer will take care of giving the URB back. When a device is disconnected, the xHCI hardware structures should be freed without issuing a disable slot command (since the hardware probably won't respond to it anyway). The debugging polling loop should stop polling if the host is dying. When a device is disconnected, any pending watchdog timers are killed with del_timer_sync(). It must be synchronous so that the watchdog timer doesn't attempt to access the freed endpoint structures. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
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| host | ||
| image | ||
| misc | ||
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| wusbcore | ||
| Kconfig | ||
| Makefile | ||
| README | ||
| usb-skeleton.c | ||
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.