On 18:22-20221215, Mark Brown wrote: > On Thu, Dec 15, 2022 at 11:54:11AM -0600, Nishanth Menon wrote: > > On 16:09-20221215, Mark Brown wrote: > > > > That proposal looks really non-idiomatic and quite unusual, if there's a > > > fixed voltage supply to the LDO I'd expect to see it modeled as a fixed > > > voltage regulator. I'm not sure what the use of bypass here is trying > > > to accomplish TBH. > > > The problem is this - the default NVM in the PMIC is setup such that > > VSET value =3.3v and bypass bit set (makes sense since the vin=3.3v). > > This implies no voltage drop over the LDO? Sounds a bit suspect. Not the choice I'd probably have made ;) > > > Now the constraint is bypass bit cannot be changed without the LDO > > being switched off. > > > regulator-allow-bypass property allows us to control bypass bit, but we > > should'nt toggle it when LDO is active. Not providing the property > > implies the bit wont be toggled by regulator core either. > > > What we need is a scheme that will disable the bypass bit with the > > intent of operating the LDO with just the vset field. I did'nt find it > > possible atm.. unless I am mistaken.. > > Can the consumer just disable the supply as part of startup? Though > that's starting to feel rather board specific. There's not really a Yeah - this happens to be SDcard supply (at least in my case).. I'd rather not change the mmc host or core layer to handle a case where LDO happened to be in bypass. it is a regulator driver's problem, IMHO how to provide the stated voltage OR fail to transition the voltage. In this driver's case, it happily accepts and set the VSET voltage - for example to 1.8V, but then, since the bypass bit is set, well, voltage sticks around at 3.3v. > good place to put a board specific setup process like that in the kernel > at the minute, you'd ideally want the firmware to leave the device at > least disabled if not actually out of bypass on startup so we don't have > to deal with this. Ugh... Yeah - that would be the other option - I could plug this bypass clear in the u-boot or someplace early so that the LDO behaves Also the reason why I did'nt send the mentioned patch (or the like upstream and the patch was done just a couple of days back) were the following questions: a) Why would'nt we handle the case where bypass bit is set AND voltage change implies bypass bit needs to be disabled? (i would expect it to fail but if i did provide regulator-allow-bypass, then if bypass is set AND requested-voltage != vin-supply, then i'd have expected framework to probably disable bypass and switch voltage to new voltage - which this driver, based on it's constraint will say "nope, cant do" - but that would be better than silently telling me all good, setting vset and leaving the bypass bit on.) b) If I wanted the LDO to poweroff the bypass bit at start (define the startup hardware condition), I dont seem to have a description for that either. -- Regards, Nishanth Menon Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3 1A34 DDB5 849D 1736 249D
