Hi, On Wed, May 30, 2018 at 4:39 PM, David Collins <colli...@codeaurora.org> wrote: > Consider the case of a regulator with physical 10 mA LPM max current. Say > that modem and application processors each have a load on the regulator > that draws 9 mA. If they each respect the 10 mA limit, then they'd each > vote for LPM. The VRM block in RPMh hardware will aggregate these requests > together using a max function which will result in the regulator being set > to LPM, even though the total load is 18 mA (which would require high > power mode (HPM)). To get around this corner case, a LPM max current of 1 > uA can be used for all LDO supplies that have non-application processor > consumers. Thus, any non-zero regulator_set_load() current request will > result in setting the regulator to HPM (which is always safe).
Is there any plan to change the way this works for future versions of RPMh? > The second situation that needs board-level DRMS mode and current limit > specification is SMPS regulator AUTO mode to PWM (HPM) mode switching. > SMPS regulators should theoretically always be able to operate in AUTO > mode as it switches automatically between PWM mode (which can provide the > maximum current) and PFM mode (which supports lower current but has higher > efficiency). However, there may be board/system issues that require > switching to PWM mode for certain use cases as it has better load > regulation (i.e. no PFM ripple for lower loads) and supports more > aggressive load current steps (i.e. greater A/ns). > > If a Linux consumer requires the ability to force a given SMPS regulator > from AUTO mode into PWM mode and that SMPS is shared by other Linux > consumers (which may be the case, but at least must be guaranteed to work > architecturally), then regulator_set_load() is the only option since it > provides aggregation, where as regulator_set_mode() does not. > regulator_set_load() can be utilized in this case by specifying AUTO mode > and PWM mode as drms modes and specifying some particular AUTO mode > maximum current (that is known by the consumer) in device tree. The > consumer can then call regulator_set_load() with the imposed AUTO mode > limit + delta when PWM mode is required and a lower value when AUTO mode > is sufficient. Mark: I'm leaving this firmly in your hands. I can see David's points here. I could even believe that some of this stuff could be board specific where one board might have slightly different capacitors or they might be placed differently and might need a higher power mode to keep the signal clean. -Doug
