diff options
Diffstat (limited to 'Documentation/usb')
| -rw-r--r-- | Documentation/usb/anchors.txt | 50 | ||||
| -rw-r--r-- | Documentation/usb/callbacks.txt | 132 | ||||
| -rw-r--r-- | Documentation/usb/persist.txt | 43 | ||||
| -rw-r--r-- | Documentation/usb/usb-serial.txt | 7 |
4 files changed, 207 insertions, 25 deletions
diff --git a/Documentation/usb/anchors.txt b/Documentation/usb/anchors.txt new file mode 100644 index 000000000000..7304bcf5a306 --- /dev/null +++ b/Documentation/usb/anchors.txt @@ -0,0 +1,50 @@ +What is anchor? +=============== + +A USB driver needs to support some callbacks requiring +a driver to cease all IO to an interface. To do so, a +driver has to keep track of the URBs it has submitted +to know they've all completed or to call usb_kill_urb +for them. The anchor is a data structure takes care of +keeping track of URBs and provides methods to deal with +multiple URBs. + +Allocation and Initialisation +============================= + +There's no API to allocate an anchor. It is simply declared +as struct usb_anchor. init_usb_anchor() must be called to +initialise the data structure. + +Deallocation +============ + +Once it has no more URBs associated with it, the anchor can be +freed with normal memory management operations. + +Association and disassociation of URBs with anchors +=================================================== + +An association of URBs to an anchor is made by an explicit +call to usb_anchor_urb(). The association is maintained until +an URB is finished by (successfull) completion. Thus disassociation +is automatic. A function is provided to forcibly finish (kill) +all URBs associated with an anchor. +Furthermore, disassociation can be made with usb_unanchor_urb() + +Operations on multitudes of URBs +================================ + +usb_kill_anchored_urbs() +------------------------ + +This function kills all URBs associated with an anchor. The URBs +are called in the reverse temporal order they were submitted. +This way no data can be reordered. + +usb_wait_anchor_empty_timeout() +------------------------------- + +This function waits for all URBs associated with an anchor to finish +or a timeout, whichever comes first. Its return value will tell you +whether the timeout was reached. diff --git a/Documentation/usb/callbacks.txt b/Documentation/usb/callbacks.txt new file mode 100644 index 000000000000..7c812411945b --- /dev/null +++ b/Documentation/usb/callbacks.txt @@ -0,0 +1,132 @@ +What callbacks will usbcore do? +=============================== + +Usbcore will call into a driver through callbacks defined in the driver +structure and through the completion handler of URBs a driver submits. +Only the former are in the scope of this document. These two kinds of +callbacks are completely independent of each other. Information on the +completion callback can be found in Documentation/usb/URB.txt. + +The callbacks defined in the driver structure are: + +1. Hotplugging callbacks: + + * @probe: Called to see if the driver is willing to manage a particular + * interface on a device. + * @disconnect: Called when the interface is no longer accessible, usually + * because its device has been (or is being) disconnected or the + * driver module is being unloaded. + +2. Odd backdoor through usbfs: + + * @ioctl: Used for drivers that want to talk to userspace through + * the "usbfs" filesystem. This lets devices provide ways to + * expose information to user space regardless of where they + * do (or don't) show up otherwise in the filesystem. + +3. Power management (PM) callbacks: + + * @suspend: Called when the device is going to be suspended. + * @resume: Called when the device is being resumed. + * @reset_resume: Called when the suspended device has been reset instead + * of being resumed. + +4. Device level operations: + + * @pre_reset: Called when the device is about to be reset. + * @post_reset: Called after the device has been reset + +The ioctl interface (2) should be used only if you have a very good +reason. Sysfs is preferred these days. The PM callbacks are covered +separately in Documentation/usb/power-management.txt. + +Calling conventions +=================== + +All callbacks are mutually exclusive. There's no need for locking +against other USB callbacks. All callbacks are called from a task +context. You may sleep. However, it is important that all sleeps have a +small fixed upper limit in time. In particular you must not call out to +user space and await results. + +Hotplugging callbacks +===================== + +These callbacks are intended to associate and disassociate a driver with +an interface. A driver's bond to an interface is exclusive. + +The probe() callback +-------------------- + +int (*probe) (struct usb_interface *intf, + const struct usb_device_id *id); + +Accept or decline an interface. If you accept the device return 0, +otherwise -ENODEV or -ENXIO. Other error codes should be used only if a +genuine error occurred during initialisation which prevented a driver +from accepting a device that would else have been accepted. +You are strongly encouraged to use usbcore'sfacility, +usb_set_intfdata(), to associate a data structure with an interface, so +that you know which internal state and identity you associate with a +particular interface. The device will not be suspended and you may do IO +to the interface you are called for and endpoint 0 of the device. Device +initialisation that doesn't take too long is a good idea here. + +The disconnect() callback +------------------------- + +void (*disconnect) (struct usb_interface *intf); + +This callback is a signal to break any connection with an interface. +You are not allowed any IO to a device after returning from this +callback. You also may not do any other operation that may interfere +with another driver bound the interface, eg. a power management +operation. +If you are called due to a physical disconnection, all your URBs will be +killed by usbcore. Note that in this case disconnect will be called some +time after the physical disconnection. Thus your driver must be prepared +to deal with failing IO even prior to the callback. + +Device level callbacks +====================== + +pre_reset +--------- + +int (*pre_reset)(struct usb_interface *intf); + +Another driver or user space is triggering a reset on the device which +contains the interface passed as an argument. Cease IO and save any +device state you need to restore. + +If you need to allocate memory here, use GFP_NOIO or GFP_ATOMIC, if you +are in atomic context. + +post_reset +---------- + +int (*post_reset)(struct usb_interface *intf); + +The reset has completed. Restore any saved device state and begin +using the device again. + +If you need to allocate memory here, use GFP_NOIO or GFP_ATOMIC, if you +are in atomic context. + +Call sequences +============== + +No callbacks other than probe will be invoked for an interface +that isn't bound to your driver. + +Probe will never be called for an interface bound to a driver. +Hence following a successful probe, disconnect will be called +before there is another probe for the same interface. + +Once your driver is bound to an interface, disconnect can be +called at any time except in between pre_reset and post_reset. +pre_reset is always followed by post_reset, even if the reset +failed or the device has been unplugged. + +suspend is always followed by one of: resume, reset_resume, or +disconnect. diff --git a/Documentation/usb/persist.txt b/Documentation/usb/persist.txt index df54d645cbb5..d56cb1a11550 100644 --- a/Documentation/usb/persist.txt +++ b/Documentation/usb/persist.txt @@ -2,7 +2,7 @@ Alan Stern <stern@rowland.harvard.edu> - September 2, 2006 (Updated May 29, 2007) + September 2, 2006 (Updated February 25, 2008) What is the problem? @@ -65,9 +65,10 @@ much better.) What is the solution? -Setting CONFIG_USB_PERSIST will cause the kernel to work around these -issues. It enables a mode in which the core USB device data -structures are allowed to persist across a power-session disruption. +The kernel includes a feature called USB-persist. It tries to work +around these issues by allowing the core USB device data structures to +persist across a power-session disruption. + It works like this. If the kernel sees that a USB host controller is not in the expected state during resume (i.e., if the controller was reset or otherwise had lost power) then it applies a persistence check @@ -80,28 +81,30 @@ re-enumeration shows that the device now attached to that port has the same descriptors as before, including the Vendor and Product IDs, then the kernel continues to use the same device structure. In effect, the kernel treats the device as though it had merely been reset instead of -unplugged. +unplugged. The same thing happens if the host controller is in the +expected state but a USB device was unplugged and then replugged. If no device is now attached to the port, or if the descriptors are different from what the kernel remembers, then the treatment is what you would expect. The kernel destroys the old device structure and behaves as though the old device had been unplugged and a new device -plugged in, just as it would without the CONFIG_USB_PERSIST option. +plugged in. The end result is that the USB device remains available and usable. Filesystem mounts and memory mappings are unaffected, and the world is now a good and happy place. -Note that even when CONFIG_USB_PERSIST is set, the "persist" feature -will be applied only to those devices for which it is enabled. You -can enable the feature by doing (as root): +Note that the "USB-persist" feature will be applied only to those +devices for which it is enabled. You can enable the feature by doing +(as root): echo 1 >/sys/bus/usb/devices/.../power/persist where the "..." should be filled in the with the device's ID. Disable the feature by writing 0 instead of 1. For hubs the feature is -automatically and permanently enabled, so you only have to worry about -setting it for devices where it really matters. +automatically and permanently enabled and the power/persist file +doesn't even exist, so you only have to worry about setting it for +devices where it really matters. Is this the best solution? @@ -112,19 +115,19 @@ centralized Logical Volume Manager. Such a solution would allow you to plug in a USB flash device, create a persistent volume associated with it, unplug the flash device, plug it back in later, and still have the same persistent volume associated with the device. As such -it would be more far-reaching than CONFIG_USB_PERSIST. +it would be more far-reaching than USB-persist. On the other hand, writing a persistent volume manager would be a big job and using it would require significant input from the user. This solution is much quicker and easier -- and it exists now, a giant point in its favor! -Furthermore, the USB_PERSIST option applies to _all_ USB devices, not +Furthermore, the USB-persist feature applies to _all_ USB devices, not just mass-storage devices. It might turn out to be equally useful for other device types, such as network interfaces. - WARNING: Using CONFIG_USB_PERSIST can be dangerous!! + WARNING: USB-persist can be dangerous!! When recovering an interrupted power session the kernel does its best to make sure the USB device hasn't been changed; that is, the same @@ -133,10 +136,10 @@ aren't guaranteed to be 100% accurate. If you replace one USB device with another of the same type (same manufacturer, same IDs, and so on) there's an excellent chance the -kernel won't detect the change. Serial numbers and other strings are -not compared. In many cases it wouldn't help if they were, because -manufacturers frequently omit serial numbers entirely in their -devices. +kernel won't detect the change. The serial number string and other +descriptors are compared with the kernel's stored values, but this +might not help since manufacturers frequently omit serial numbers +entirely in their devices. Furthermore it's quite possible to leave a USB device exactly the same while changing its media. If you replace the flash memory card in a @@ -152,5 +155,5 @@ but yourself. YOU HAVE BEEN WARNED! USE AT YOUR OWN RISK! That having been said, most of the time there shouldn't be any trouble -at all. The "persist" feature can be extremely useful. Make the most -of it. +at all. The USB-persist feature can be extremely useful. Make the +most of it. diff --git a/Documentation/usb/usb-serial.txt b/Documentation/usb/usb-serial.txt index 8b077e43eee7..ff2c1ff57ba2 100644 --- a/Documentation/usb/usb-serial.txt +++ b/Documentation/usb/usb-serial.txt @@ -192,12 +192,9 @@ Keyspan USA-series Serial Adapters FTDI Single Port Serial Driver - This is a single port DB-25 serial adapter. More information about this - device and the Linux driver can be found at: - http://reality.sgi.com/bryder_wellington/ftdi_sio/ + This is a single port DB-25 serial adapter. - For any questions or problems with this driver, please contact Bill Ryder - at bryder@sgi.com + For any questions or problems with this driver, please contact Bill Ryder. ZyXEL omni.net lcd plus ISDN TA |