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usb_wait_anchor_empty_timeout() should wait till the completion handler has run. Both the zd1211rw driver and the uas driver (in its task mgmt) depend on the completion handler having completed when usb_wait_anchor_empty_timeout() returns, as they read state set by the completion handler after an usb_wait_anchor_empty_timeout() call. But __usb_hcd_giveback_urb() calls usb_unanchor_urb before calling the completion handler. This is necessary as the completion handler may re-submit and re-anchor the urb. But this introduces a race where the state these drivers want to read has not been set yet by the completion handler (this race is easily triggered with the uas task mgmt code). I've considered adding an anchor_count to struct urb, which would be incremented on anchor and decremented on unanchor, and then only actually do the anchor / unanchor on 0 -> 1 and 1 -> 0 transtions, combined with moving the unanchor call in hcd_giveback_urb to after calling the completion handler. But this will only work if urb's are only re-anchored to the same anchor as they were anchored to before the completion handler ran. And at least one driver re-anchors to another anchor from the completion handler (rtlwifi). So I have come up with this patch instead, which adds the ability to suspend wakeups of usb_wait_anchor_empty_timeout() waiters to the usb_anchor functionality, and uses this in __usb_hcd_giveback_urb() to delay wake-ups until the completion handler has run. Signed-off-by: Hans de Goede <hdegoede@redhat.com> Acked-by: Oliver Neukum <oliver@neukum.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| 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.