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The Panther Point chipset has an xHCI host controller that has a limit to the number of active endpoints it can handle. Ideally, it would signal that it can't handle anymore endpoints by returning a Resource Error for the Configure Endpoint command, but they don't. Instead it needs software to keep track of the number of active endpoints, across configure endpoint commands, reset device commands, disable slot commands, and address device commands. Add a new endpoint context counter, xhci_hcd->num_active_eps, and use it to track the number of endpoints the xHC has active. This gets a little tricky, because commands to change the number of active endpoints can fail. This patch adds a new xHCI quirk for these Intel hosts, and the new code should not have any effect on other xHCI host controllers. Fail a new device allocation if we don't have room for the new default control endpoint. Use the endpoint ring pointers to determine what endpoints were active before a Reset Device command or a Disable Slot command, and drop those once the command completes. Fail a configure endpoint command if it would add too many new endpoints. We have to be a bit over zealous here, and only count the number of new endpoints to be added, without subtracting the number of dropped endpoints. That's because a second configure endpoint command for a different device could sneak in before we know if the first command is completed. If the first command dropped resources, the host controller fails the command for some reason, and we're nearing the limit of endpoints, we could end up oversubscribing the host. To fix this race condition, when evaluating whether a configure endpoint command will fix in our bandwidth budget, only add the new endpoints to xhci->num_active_eps, and don't subtract the dropped endpoints. Ignore changed endpoints (ones that are dropped and then re-added), as that shouldn't effect the host's endpoint resources. When the configure endpoint command completes, subtract off the dropped endpoints. This may mean some configuration changes may temporarily fail, but it's always better to under-subscribe than over-subscribe resources. (Originally my plan had been to push the resource allocation down into the ring allocation functions. However, that would cause us to allocate unnecessary resources when endpoints were changed, because the xHCI driver allocates a new ring for the changed endpoint, and only deletes the old ring once the Configure Endpoint command succeeds. A further complication would have been dealing with the per-device endpoint ring cache.) Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
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.