forked from Minki/linux
7027df36e4
Unconditionally wake up the child device when the power session is recovered. This addresses the following scenarios: 1/ The device may need a reset on power-session loss, without this change port power-on recovery exposes khubd to scenarios that usb_port_resume() is set to handle. Prior to port power control the only time a power session would be lost is during dpm_suspend of the hub. In that scenario usb_port_resume() is guaranteed to be called prior to khubd running for that port. With this change we wakeup the child device as soon as possible (prior to khubd running again for this port). Although khubd has facilities to wake a child device it will only do so if the portstatus / portchange indicates a suspend state. In the case of port power control we are not coming from a hub-port-suspend state. This implementation simply uses pm_request_resume() to wake the device and relies on the port_dev->status_lock to prevent any collisions between khubd and usb_port_resume(). 2/ This mechanism rate limits port power toggling. The minimum port power on/off period is now gated by the child device suspend/resume latency. Empirically this mitigates devices downgrading their connection on perceived instability of the host connection. This ratelimiting is really only relevant to port power control testing, but it is a nice side effect of closing the above race. Namely, the race of khubd for the given port running while a usb_port_resume() event is pending. 3/ Going forward we are finding that power-session recovery requires warm-resets (http://marc.info/?t=138659232900003&r=1&w=2). This mechanism allows for warm-resets to be requested at the same point in the resume path for hub dpm_suspend power session losses, or port rpm_suspend power session losses. 4/ If the device *was* disconnected the only time we'll know for sure is after a failed resume, so it's necessary for usb_port_runtime_resume() to expedite a usb_port_resume() to clean up the removed device. The reasoning for this is "least surprise" for the user. Turning on a port means that hotplug detection is again enabled for the port, it is surprising that devices that were removed while the port was off are not disconnected until they are attempted to be used. As a user "why would I try to use a device I removed from the system?" 1, 2, and 4 are not a problem in the system dpm_resume() case because, although the power-session is lost, khubd is frozen until after device resume. For the rpm_resume() case pm_request_resume() is used to request re-validation of the device, and if it happens to collide with a khubd run we rely on the port_dev->status_lock to synchronize those operations. Besides testing, the primary scenario where this mechanism is expected to be triggered is when the user changes the port power policy (control/pm_qos_no_poweroff, or power/control). Each time power is enabled want to revalidate the child device, where the revalidation is handled by usb_port_resume(). Given that this arranges for port_dev->child to be de-referenced in usb_port_runtime_resume() we need to make sure not to collide with usb_disconnect() that frees the usb_device. To this end we hold the port active with the "child_usage" reference across the disconnect event. Subsequently, the need to access hub->child_usage_bits lead to the creation of hub_disconnect_children() to remove any ambiguity of which "hub" is being acted on in usb_disconnect() (prompted-by sharp eyes from Alan). Cc: Rafael J. Wysocki <rjw@rjwysocki.net> Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| atm | ||
| c67x00 | ||
| chipidea | ||
| class | ||
| common | ||
| core | ||
| dwc2 | ||
| dwc3 | ||
| early | ||
| gadget | ||
| host | ||
| image | ||
| misc | ||
| mon | ||
| musb | ||
| phy | ||
| renesas_usbhs | ||
| serial | ||
| storage | ||
| wusbcore | ||
| Kconfig | ||
| Makefile | ||
| README | ||
| 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.