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xhci DbC driver polls the host controller for DbC events at a reduced
rate when DbC is enabled but there are no active data transfers.
Allow users to modify this reduced poll interval via dbc_poll_interval_ms
sysfs entry. Unit is milliseconds and accepted range is 0 to 5000.
Max interval of 5000 ms is selected as it matches the common 5 second
timeout used in usb stack.
Default value is 64 milliseconds.
A long interval is useful when users know there won't be any activity
on systems connected via DbC for long periods, and want to avoid
battery drainage due to unnecessary CPU usage.
Example being Android Debugger (ADB) usage over DbC on ChromeOS systems
running Android Runtime.
[minor changes and rewording -Mathias]
Co-developed-by: Samuel Jacob <samjaco@google.com>
Signed-off-by: Samuel Jacob <samjaco@google.com>
Signed-off-by: Uday M Bhat <uday.m.bhat@intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20240626124835.1023046-5-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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When DbC is enabled the first port on the xHC host acts as a usb device.
xHC provides the descriptors automatically when the DbC device is
enumerated. Most of the values are hardcoded, but some fields such as
idProduct, idVendor, bcdDevice and bInterfaceProtocol can be modified.
Add sysfs entries that allow userspace to change these.
User can only change them before dbc is enabled, i.e. before writing
"enable" to dbc sysfs file as we don't want these values to change while
device is connected, or during enumeration.
Add documentation for these entries in
Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20230317154715.535523-9-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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xHCI compatible USB host controllers(i.e. super-speed USB3 controllers)
can be implemented with the Debug Capability(DbC). It presents a debug
device which is fully compliant with the USB framework and provides the
equivalent of a very high performance full-duplex serial link. The debug
capability operation model and registers interface are defined in 7.6.8
of the xHCI specification, revision 1.1.
The DbC debug device shares a root port with the xHCI host. By default,
the debug capability is disabled and the root port is assigned to xHCI.
When the DbC is enabled, the root port will be assigned to the DbC debug
device, and the xHCI sees nothing on this port. This implementation uses
a sysfs node named <dbc> under the xHCI device to manage the enabling
and disabling of the debug capability.
When the debug capability is enabled, it will present a debug device
through the debug port. This debug device is fully compliant with the
USB3 framework, and it can be enumerated by a debug host on the other
end of the USB link. As soon as the debug device is configured, a TTY
serial device named /dev/ttyDBC0 will be created.
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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