On Wed, Apr 15, 2009 at 11:29:01AM -0400, Alan Stern wrote: > On Tue, 14 Apr 2009, [utf-8] Arve Hjønnevåg wrote: > > > +Suspend blockers can be used to allow user-space to decide which keys should > > +wake the full system up and turn the screen on. > > This sentence still grates on me. For readers not familiar with the > embedded/phone environment, it won't make any sense. Furthermore the > rest of the text below doesn't even mention the screen, which will > cause readers to wonder why it is mentioned here. > > > Use set_irq_wake or a platform > > +specific api to make sure the keypad interrupt wakes up the cpu. Once the keypad > > +driver has resumed, the sequence of events can look like this: > > +- 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. It determines that the > > + key should not wake up the full system, calls suspend_unblock on the > > + process-input-events suspend_blocker and calls select or poll. > > + > > + Key pressed Key released > > + | | > > +keypad-scan ++++++++++++++++++ > > +input-event-queue +++ +++ > > +process-input-events +++ +++ > > How about replacing that first sentence with something like this: > > In cell phones or other embedded systems where powering the > screen is a significant drain on the battery, suspend blockers > can be used to allow user-space to decide whether a keystroke > received while the system is suspended should cause the screen > to be turned back on or allow the system to go back into > suspend. > > Then in the last section, say this: > > - The user-space input-event thread returns from read. If it > determines that the key should leave the screen off, 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. I'm still re-reviewing the design so I probably should keep my mouth shut, but I only see code for constraining entry into suspend state (S3 if you will) I didn't see code that would get called to block device entry into higher power states just constraints on entire system entry into sleep state. (I apologize if I missed that code and will happily eat my words if needed.) more comments after I finish looking over the code. --mgross _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
