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It has been requested that usbfs should implement runtime power management, instead of forcing the device to remain at full power as long as the device file is open. This patch introduces that new feature. It does so by adding three new usbfs ioctls: USBDEVFS_FORBID_SUSPEND: Prevents the device from going into runtime suspend (and causes a resume if the device is already suspended). USBDEVFS_ALLOW_SUSPEND: Allows the device to go into runtime suspend. Some time may elapse before the device actually is suspended, depending on things like the autosuspend delay. USBDEVFS_WAIT_FOR_RESUME: Blocks until the call is interrupted by a signal or at least one runtime resume has occurred since the most recent ALLOW_SUSPEND ioctl call (which may mean immediately, even if the device is currently suspended). In the latter case, the device is prevented from suspending again just as if FORBID_SUSPEND was called before the ioctl returns. For backward compatibility, when the device file is first opened runtime suspends are forbidden. The userspace program can then allow suspends whenever it wants, and either resume the device directly (by forbidding suspends again) or wait for a resume from some other source (such as a remote wakeup). URBs submitted to a suspended device will fail or will complete with an appropriate error code. This combination of ioctls is sufficient for user programs to have nearly the same degree of control over a device's runtime power behavior as kernel drivers do. Still lacking is documentation for the new ioctls. I intend to add it later, after the existing documentation for the usbfs userspace API is straightened out into a reasonable form. Suggested-by: Mayuresh Kulkarni <mkulkarni@opensource.cirrus.com> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1908071013220.1514-100000@iolanthe.rowland.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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