On Sat, 9 Oct 2010, Rafael J. Wysocki wrote: > On Wednesday, October 06, 2010, Alan Stern wrote: > > On Wed, 6 Oct 2010, Rafael J. Wysocki wrote: > > > > > > Mobile folks wish to power down some devices (most often input - > > > > touchscreen, keypad) under certain circumstances to save power. > > > > So far they were doing that by adding "disable" hook to individual > > > > drivers and while I did allow that in for some devices I feel that we > > > > need more standardised solution, preferably one that could re-use > > > > existing PM hooks in drivers. > > > > > > There's no interface for that at the PM core level, but I think we should > > > add it, perhaps in analogy to the autosuspend one. Namely, we can add a > > > flag for drivers who want to make their suspend/resume callbacks to be > > > reachable directly from user space. Setting that flag would enable a sysfs > > > attribute in /sys/devices/.../power/ allowing user space to invoke > > > pm_runtime_suspend() and pm_runtime_resume() for the given device. > > > > We already have power/control. If the subsystem sets it to "on" by > > default and the driver suspends the device whenever it is idle, then > > userspace can control the power level by writing "auto" or "on" to > > power/control. > > The problem is that with the 'auto' setting the driver decides when to suspend > and the driver need not know it's the right time. > > Suspending a graphics adapter when the user presses a "turn screen off" > button it a good example of this. The graphics driver may not know the button > was pressed and it has to be told about that. OTOH the button driver need > not know what exactly should be done when it is pressed. There may be a user > space component in between that processes the button event and should be able > to tell the graphics driver to suspend. You are clearly right; userspace has to tell the driver when it is okay to suspend. My point was that we already have a mechanism in the PM core for doing this -- assuming the driver is written appropriately (to assume that it should try to suspend whenever possible). We shouldn't need to add another mechanism. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
