Lines Matching +full:power +full:- +full:on +full:- +full:reset

1 .. _usb-persist:
14 bus must continue to supply suspend current (around 1-5 mA).  This
16 detect connect-change events (devices being plugged in or unplugged).
17 The technical term is "power session".
19 If a USB device's power session is interrupted then the system is
27 controller loses power during a system suspend, then when the system
35 system woke up, who cares?  It'll still work the same when you type on
38 Unfortunately problems _can_ arise, particularly with mass-storage
41 filesystem on the device, you're out of luck -- everything in that
43 root filesystem was located on the device, since your system will
46 Loss of power isn't the only mechanism to worry about.  Anything that
47 interrupts a power session will have the same effect.  For example,
49 was asleep, on many systems during the initial stages of wakeup the
51 controllers.  Result: all the power sessions are destroyed and again
56 On many systems the USB host controllers will get reset after a
57 suspend-to-RAM.  On almost all systems, no suspend current is
58 available during hibernation (also known as swsusp or suspend-to-disk).
60 has happened; look for lines saying "root hub lost power or was reset".
62 In practice, people are forced to unmount any filesystems on a USB
63 device before suspending.  If the root filesystem is on a USB device,
65 suspended -- but it will crash as soon as it wakes up, which isn't
72 The kernel includes a feature called USB-persist.  It tries to work
74 persist across a power-session disruption.
78 reset or otherwise had lost power) then it applies a persistence check
81 can't work once the power session is gone.  Instead it issues a USB
82 port reset and then re-enumerates the device.  (This is exactly the
83 same thing that happens whenever a USB device is reset.)  If the
84 re-enumeration shows that the device now attached to that port has the
87 kernel treats the device as though it had merely been reset instead of
104 Note that the "USB-persist" feature will be applied only to those
108 	echo 1 >/sys/bus/usb/devices/.../power/persist
112 automatically and permanently enabled and the power/persist file
126 it would be more far-reaching than USB-persist.
128 On the other hand, writing a persistent volume manager would be a big
130 solution is much quicker and easier -- and it exists now, a giant
133 Furthermore, the USB-persist feature applies to _all_ USB devices, not
134 just mass-storage devices.  It might turn out to be equally useful for
138 WARNING: USB-persist can be dangerous!!
141 When recovering an interrupted power session the kernel does its best
147 manufacturer, same IDs, and so on) there's an excellent chance the
165 maybe fail because they may morph after reset.
170 at all.  The USB-persist feature can be extremely useful.  Make the