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commit ed18c5fa94 upstream.
This optimization significantly reduces xhci driver load time.
In ACPI tables the acpi companion port devices are children of
the hub device. The port devices are identified by their port number
returned by the ACPI _ADR method.
_ADR 0 is reserved for the root hub device.
The current implementation to find a acpi companion port device
loops through all acpi port devices under that parent hub, evaluating
their _ADR method each time a new port device is added.
for a xHC controller with 25 ports under its roothub it
will end up invoking ACPI bytecode 625 times before all ports
are ready, making it really slow.
The _ADR values are already read and cached earler. So instead of
running the bytecode again we can check the cached _ADR value first,
and then fall back to the old way.
As one of the more significant changes, the xhci load time on
Intel kabylake reduced by 70%, (28ms) from
initcall xhci_pci_init+0x0/0x49 returned 0 after 39537 usecs
to
initcall xhci_pci_init+0x0/0x49 returned 0 after 11270 usecs
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 ("hub_wq").
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.