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The RWE bit of the USB 2.0 PORTPMSC register is supposed to enable
remote wakeup for devices in the lower power link state L1. It has
nothing to do with the device suspend remote wakeup from L2. The RWE
bit is designed to be set once (when USB 2.0 LPM is enabled for the
port) and cleared only when USB 2.0 LPM is disabled for the port.
The xHCI bus suspend method was setting the RWE bit erroneously, and the
bus resume method was clearing it. The xHCI 1.0 specification with
errata up to Aug 12, 2012 says in section 4.23.5.1.1.1 "Hardware
Controlled LPM":
"While Hardware USB2 LPM is enabled, software shall not modify the
HIRDBESL or RWE fields of the USB2 PORTPMSC register..."
If we have previously enabled USB 2.0 LPM for a device, that means when
the USB 2.0 bus is resumed, we violate the xHCI specification by
clearing RWE. It also means that after a bus resume, the host would
think remote wakeup is disabled from L1 for ports with USB 2.0 Link PM
enabled, which is not what we want.
This patch should be backported to kernels as old as 3.2, that
contain the commit
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| .. | ||
| atm | ||
| c67x00 | ||
| chipidea | ||
| class | ||
| core | ||
| dwc3 | ||
| early | ||
| gadget | ||
| host | ||
| image | ||
| misc | ||
| mon | ||
| musb | ||
| phy | ||
| renesas_usbhs | ||
| serial | ||
| storage | ||
| wusbcore | ||
| Kconfig | ||
| Makefile | ||
| README | ||
| usb-common.c | ||
| usb-skeleton.c | ||
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.