On Fri, 25 Jun 2021, Douglas Anderson wrote: > The regulator for the touchscreen could be: > * A dedicated regulator just for the touchscreen. > * A regulator shared with something else in the system. > * An always-on regulator. > > How we want the "reset" line to behave depends a bit on which of those > three cases we're in. Currently the code is written with the > assumption that it has a dedicated regulator, but that's not really > guaranteed to be the case. > > The problem we run into is that if we leave the touchscreen powered on > (because someone else is requesting the regulator or it's an always-on > regulator) and we assert reset then we apparently burn an extra 67 mW > of power. That's not great. > > Let's instead tie the control of the reset line to the true state of > the regulator as reported by regulator notifiers. If we have an > always-on regulator our notifier will never be called. If we have a > shared regulator then our notifier will be called when the touchscreen > is truly turned on or truly turned off. > > Using notifiers like this nicely handles all the cases without > resorting to hacks like pretending that there is no "reset" GPIO if we > have an always-on regulator. > > NOTE: if the regulator is on a shared line it's still possible that > things could be a little off. Specifically, this case is not handled > even after this patch: > 1. Suspend goodix (send "sleep", goodix stops requesting regulator on) > 2. Other regulator user turns off (regulator fully turns off). > 3. Goodix driver gets notified and asserts reset. > 4. Other regulator user turns on. > 5. Goodix driver gets notified and deasserts reset. > 6. Nobody resumes goodix. > > With that set of steps we'll have reset deasserted but we will have > lost the results of the I2C_HID_PWR_SLEEP from the suspend path. That > means we might be in higher power than we could be even if the goodix > driver thinks things are suspended. Presumably, however, we're still > in better shape than if we were asserting "reset" the whole time. If > somehow the above situation is actually affecting someone and we want > to do better we can deal with it when we have a real use case. > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> Applied, thanks Doug. -- Jiri Kosina SUSE Labs
