On Saturday 15 August 2009, Alan Stern wrote: > On Sat, 15 Aug 2009, Rafael J. Wysocki wrote: > > > > > Why don't we add a flag indicating whether or not the device is allowed to > > > > be power managed at run time, something like runtime_forbidden, that the > > > > user space will be able to set through sysfs? > > > > > > I think even having a runtime_wakeup flag (which defaults to on) would > > > be sufficient. > > > > Perhaps it would, but then unsetting runtime_wakeup would effectively disable > > runtime PM for devices that need it to be power managed at run time (probably > > all input devices). Also there may be situations in which user space may > > really want to disable runtime PM for some devices (think of broken hardware > > for one example). > > It sounds like there are really three choices here, and the decision > should largely be left up to the user: > > 1. don't use runtime PM, > > 2. allow runtime PM but disable remote wakeup, > > 3. allow runtime PM with remote wakeup enabled. > > Now, a driver may say "I can't do my job without remote wakeup". Such > a driver would refuse to do runtime_suspend in case 2. But otherwise > we should follow the preference of the user. > > The only remaining question is how to expose this in sysfs in a way > that won't be confusing and that won't be confused with the "wakeup" > attribute. One possibility is to use the "level" attribute introduced > in USB; possible levels are "on" (no runtime PM) and "auto" (runtime > PM allowed). Then a new "runtime_wakeup" attribute could contain > nothing (if wakeup is not available), "enabled", or "disabled". That seems to require two flags. runtime_forbidden - if unset, the driver decides whether or not to use runtime PM; that could be exposed through sysfs as 'runtime' under the 'power' subdirectory with the following values: * 'disabled' - runtime_forbidden is set by the user space * 'on' - runtime_forbidden is unset, runtime PM is used (disable_depth == 0) * 'off' - runtime_forbidden is unset, runtime PM is not used To set/unset the user space writes 'enabled'/'disabled' to it, respectively. The default is unset. runtime_wakeup - if set, the device is allowed to do remote wakeup at run time That could be represented as 'runtime_wakeup' under 'power' with the following values: * no value (empty file) is 'runtime' is 'disabled' * 'enabled' * 'disabled' To set/unset the user space writes 'enabled'/'disabled' to it, respectively. The default is set. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
