On Sun, Oct 10, 2010 at 04:34:38PM -0400, Alan Stern wrote: > On Sun, 10 Oct 2010, Rafael J. Wysocki wrote: > > > > > > > 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. > > ... > > > > 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. > > > > OK, so how is a graphics driver going to figure out it should suspend when the > > button is pressed in the example above? > > The graphics driver doesn't have to figure that out at all. It merely > has to suspend the display whenever it can, i.e., whenever the usage > count drops to 0 (or equivalently, whenever the runtime_idle callback > runs). That makes sense for drivers that do very agressive PM, but fails for cases when you have bigger timeouts. My phone shuts off its display automatically after 30 seconds or a minute but I have an option of pressing a button which causes it to shut off immediately. > > It's up to userspace to make sure that the display's usage count goes > to 0 at the proper time, i.e., when the button is pressed. Contrary to > what you wrote above, we _do_ have an interface for this at the PM core > level: power/control. > I think that while using power/control is a _very_ good option "auto" and "on" are not enough, we need 3 states: "on", "off" and "auto". Thanks. -- Dmitry -- 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
