On 05/13/2015 10:16 AM, Mark Brown wrote: > On Wed, May 13, 2015 at 10:00:41AM -0500, Nishanth Menon wrote: > >> What I dont see in the thread, and the point I raised here, why have >> nominal/typical voltage at all? min<->max should be sufficient, >> correct? If the device cannot function at min, then it should not be >> documented as part of valid range at all. > > Going for the minimum specified voltage is asking for trouble with > regard to tolerances and so on, see also your concern about process > corners. If the electrical engineers specify things as X +/- Y the > most conservative thing to do is to try to hit X rather than going > straight for the limits. I've had the same debate with my company's SoC designers as well on various occasions as well. At least for the SoCs I deal with, X +/- Y range specification involves PMIC/Board variations, where X is the least voltage that is attempted to be set on PMIC, X-Y is the min voltage allowed at the SoC ball, due to SMPS noise/IRDrop and other board specific behavior. I am not saying all SoC vendors do specifications the same way, but our interest from device tree description is the operating voltage range for the device that we can control on the PMIC. if setting (X-Y) is not stable voltage for the device, then it should not be stated in the description. To illustrate: What does it mean for a driver using regulator API? Attempt X <-> (X+Y), if that fails (example PMIC SMPS max < X), try (X-Y)<->(X)? If yes, then we do expect (X-Y)<->(X+Y) should be stable for all operating conditions for the device, correct? If this is is not stable at (X-Y), then we have a wrong specification for the device for claiming X +/- Y is a valid range for the device. -- Regards, Nishanth Menon -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
