Mike, On 05/12/2015 02:01 PM, Michael Turquette wrote: > Quoting Viresh Kumar (2015-05-11 22:20:33) >> On 10-05-15, 20:07, Nishanth Menon wrote: >>> just one minor concern being in the SoC end of the world :). In most >>> times, the current consumption for a specific OPP varies depending on >>> the specific location in the process node the die is -> this is even >>> true among a single lot of wafers as well. some SoC vendors use hot, >>> nominal and cold terminology to indicate the characteristics of the >>> specific sample. >>> >>> it might help state which sample end of the spectrum we are talking >>> about here. reason being: if I put in values based on my board >>> measurement, the results may not be similar to what someone else's >>> sample be. Depending on technology, speed binning strategy used by the >>> vendor, temperature and few other characteristics, these numbers could >>> be widely divergent. >> >> I don't have any clue about this.. :( >> >> @Mark/stephen: Any inputs ? > > I do not think the idea of the mA property is to perfectly model current > consumption at a given opp. Instead it is a nominal value that may be > useful, e.g. for configuring a regulator in Stephen's case. > > The TWLxxxx series of PMICs from TI have configurable SMPS which could > possibly benefit from this info as well. Most of the time those are left > in an "automatic mode", but there are manual programming steps to > achieve higher efficiencies and this property could potentially help you > do that. While TWLxx series was kind of nascent in it's ability of choosing PWM/PFM or auto mode depending on the current targets, newer PMICs have their own unique techniques -> but, that said, this is a description of power consumption for a given OPP for the "device", How would stephen's case work with a PMIC and 2 devices which have different leakage characteristics (based on which end of the process spectrum they come from), Lets take an example: device X consumes 800mA for OPPx device Y consumes 900mA for OPPy Taking the simpler example of TWLxxx, the PMIC switches to PWM mode at 850mA for efficiency reasons, below 850mA, it is better to operate for accuracy and efficiency reasons at PFM mode. by putting 800mA we break efficiency on device Y, and if we choose to put 900mA or 850mA, we break efficiency on device X. It is a lot more impactful than using relative numbers for other purposes - for example energy aware scheduling as an example -> here the actuals might have better optimization, but hints of relative power numbers by itself is pretty powerful information to help scheduling. The usage, in this case, unlike the usage for a PMIC efficiency selection, is not based on absolutes and is meant more of a hint (closer to usage such as clock transition latency numbers). This is the reason I suggested to have a clear guidance in the bindings, since we'd very much like bindings to be ABI. -- 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
