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Hub-initiated LPM is not good for USB communications devices. Comms devices should be able to tell when their link can go into a lower power state, because they know when an incoming transmission is finished. Ideally, these devices would slam their links into a lower power state, using the device-initiated LPM, after finishing the last packet of their data transfer. If we enable the idle timeouts for the parent hubs to enable hub-initiated LPM, we will get a lot of useless LPM packets on the bus as the devices reject LPM transitions when they're in the middle of receiving data. Worse, some devices might blindly accept the hub-initiated LPM and power down their radios while they're in the middle of receiving a transmission. The Intel Windows folks are disabling hub-initiated LPM for all USB communications devices under a xHCI USB 3.0 host. In order to keep the Linux behavior as close as possible to Windows, we need to do the same in Linux. Set the disable_hub_initiated_lpm flag for for all USB communications drivers. I know there aren't currently any USB 3.0 devices that implement these class specifications, but we should be ready if they do. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Cc: Marcel Holtmann <marcel@holtmann.org> Cc: Gustavo Padovan <gustavo@padovan.org> Cc: Johan Hedberg <johan.hedberg@gmail.com> Cc: Hansjoerg Lipp <hjlipp@web.de> Cc: Tilman Schmidt <tilman@imap.cc> Cc: Karsten Keil <isdn@linux-pingi.de> Cc: Peter Korsgaard <jacmet@sunsite.dk> Cc: Jan Dumon <j.dumon@option.com> Cc: Petko Manolov <petkan@users.sourceforge.net> Cc: Steve Glendinning <steve.glendinning@smsc.com> Cc: "John W. Linville" <linville@tuxdriver.com> Cc: Kalle Valo <kvalo@qca.qualcomm.com> Cc: "Luis R. Rodriguez" <mcgrof@qca.qualcomm.com> Cc: Jouni Malinen <jouni@qca.qualcomm.com> Cc: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com> Cc: Senthil Balasubramanian <senthilb@qca.qualcomm.com> Cc: Christian Lamparter <chunkeey@googlemail.com> Cc: Brett Rudley <brudley@broadcom.com> Cc: Roland Vossen <rvossen@broadcom.com> Cc: Arend van Spriel <arend@broadcom.com> Cc: "Franky (Zhenhui) Lin" <frankyl@broadcom.com> Cc: Kan Yan <kanyan@broadcom.com> Cc: Dan Williams <dcbw@redhat.com> Cc: Jussi Kivilinna <jussi.kivilinna@mbnet.fi> Cc: Ivo van Doorn <IvDoorn@gmail.com> Cc: Gertjan van Wingerde <gwingerde@gmail.com> Cc: Helmut Schaa <helmut.schaa@googlemail.com> Cc: Herton Ronaldo Krzesinski <herton@canonical.com> Cc: Hin-Tak Leung <htl10@users.sourceforge.net> Cc: Larry Finger <Larry.Finger@lwfinger.net> Cc: Chaoming Li <chaoming_li@realsil.com.cn> Cc: Daniel Drake <dsd@gentoo.org> Cc: Ulrich Kunitz <kune@deine-taler.de> 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.