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The hub driver was recently changed to use "global" suspend for system suspend transitions on non-SuperSpeed buses. This means that we don't suspend devices individually by setting the suspend feature on the upstream hub port; instead devices all go into suspend automatically when the root hub stops transmitting packets. The idea was to save time and to avoid certain kinds of wakeup races. Now it turns out that many hubs are buggy; they don't relay wakeup requests from a downstream port to their upstream port if the downstream port's suspend feature is not set (depending on the speed of the downstream port, whether or not the hub is enabled for remote wakeup, and possibly other factors). We can't have hubs dropping wakeup requests. Therefore this patch goes partway back to the old policy: It sets the suspend feature for a port if the device attached to that port or any of its descendants is enabled for wakeup. People will still be able to benefit from the time savings if they don't care about wakeup and leave it disabled on all their devices. In order to accomplish this, the patch adds a new field to the usb_hub structure: wakeup_enabled_descendants is a count of how many devices below a suspended hub are enabled for remote wakeup. A corresponding new subroutine determines the number of wakeup-enabled devices at or below an arbitrary suspended USB device. This should be applied to the 3.10 stable kernel. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Reported-and-tested-by: Toralf Förster <toralf.foerster@gmx.de> Cc: stable <stable@vger.kernel.org> 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.