2012/2/11 Rafael J. Wysocki <rjw@xxxxxxx>: > Hi, > > On Saturday, January 21, 2012, Arve Hjønnevåg wrote: >> Add an ioctl, EVIOCSSUSPENDBLOCK, to block suspend while the event >> queue is not empty. This allows userspace code to process input >> events while the device appears to be asleep. > > I have two questions to start with, if you don't mind: > > (1) Does Android user space use an analogous interface right now or is it > a prototype? > Yes (for the next version), but with a wakelock based implementation. > (2) What exactly are the use cases for it (ie. what problem does it address > that cannot be addressed in a different way)? > The reason for adding an ioctl versus the old android version with used a wakelock for all input events, is that not all input events are wakeup events. Specifically some sensors generate input events at such a high rate that they prevent suspend while the sensor is on even though the driver has a suspend hook that turns the sensor off. If you are asking why input events need to block suspend at all, this was the example used in the suspend blocker documentation: - The Keypad driver gets an interrupt. It then calls suspend_block on the keypad-scan suspend_blocker and starts scanning the keypad matrix. - The keypad-scan code detects a key change and reports it to the input-event driver. - The input-event driver sees the key change, enqueues an event, and calls suspend_block on the input-event-queue suspend_blocker. - The keypad-scan code detects that no keys are held and calls suspend_unblock on the keypad-scan suspend_blocker. - The user-space input-event thread returns from select/poll, calls suspend_block on the process-input-events suspend_blocker and then calls read on the input-event device. - The input-event driver dequeues the key-event and, since the queue is now empty, it calls suspend_unblock on the input-event-queue suspend_blocker. - The user-space input-event thread returns from read. If it determines that the key should be ignored, it calls suspend_unblock on the process_input_events suspend_blocker and then calls select or poll. The system will automatically suspend again, since now no suspend blockers are active. -- Arve Hjønnevåg -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
