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The hcd->state variable is a disaster. It's not clearly owned by either usbcore or the host controller drivers, and they both change it from time to time, potentially stepping on each other's toes. It's not protected by any locks. And there's no mechanism to prevent it from going through an invalid transition. This patch (as1451) takes a first step toward fixing these problems. As it turns out, usbcore uses hcd->state for essentially only two things: checking whether the controller's root hub is running and checking whether the controller has died. Therefore the patch adds two new atomic bitflags to the hcd structure, to store these pieces of information. The new flags are used only by usbcore, and a private spinlock prevents invalid combinations (a dead controller's root hub cannot be running). The patch does not change the places where usbcore sets hcd->state, since HCDs may depend on them. Furthermore, there is one place in usb_hcd_irq() where usbcore still must use hcd->state: An HCD's interrupt handler can implicitly indicate that the controller died by setting hcd->state to HC_STATE_HALT. Nevertheless, the new code is a big improvement over the current code. The patch makes one other change. The hcd_bus_suspend() and hcd_bus_resume() routines now check first whether the host controller has died; if it has then they return immediately without calling the HCD's bus_suspend or bus_resume methods. This fixes the major problem reported in Bugzilla #29902: The system fails to suspend after a host controller dies during system resume. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Tested-by: Alex Terekhov <a.terekhov@gmail.com> CC: <stable@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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.