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d6759133e9
The current XHCI driver recalculates the Context Entries field in the Slot Context on every add_endpoint() and drop_endpoint() call. In the case of drop_endpoint(), it seems to assume that the add_flags will always contain every endpoint for the new configuration, which is not necessarily correct if you don't make assumptions about how the USB core uses the add_endpoint/drop_endpoint interface (add_flags only contains endpoints that are new additions in the new configuration). Furthermore, EP0_FLAG is not consistently set in add_flags throughout the lifetime of a device. This means that when all endpoints are dropped, the Context Entries field can be set to 0 (which is invalid and may cause a Parameter Error) or -1 (which is interpreted as 31 and causes the driver to keep using the old, incorrect value). The only surefire way to set this field right is to also take all existing endpoints into account, and to force the value to 1 (meaning only EP0 is active) if no other endpoint is found. This patch implements that as a single step in the final check_bandwidth() call and removes the intermediary calculations from add_endpoint() and drop_endpoint(). Signed-off-by: Julius Werner <jwerner@chromium.org> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.