On Mon, Aug 3, 2015 at 12:22 PM, Julian Calaby <julian.calaby@xxxxxxxxx> wrote: > Hi Chen-Yu, > > On Mon, Aug 3, 2015 at 12:37 PM, Chen-Yu Tsai <wens@xxxxxxxx> wrote: >> Hi, >> >> On Mon, Aug 3, 2015 at 7:35 AM, Julian Calaby <julian.calaby@xxxxxxxxx> wrote: >>> Hi Timo, >>> >>> On Mon, Aug 3, 2015 at 5:23 AM, Timo Sigurdsson >>> <public_timo.s@xxxxxxxxxxxxxx> wrote: >>>> sun7i-a20.dtsi contains an cpufreq operating point at 0.9 volts. Most A20 boards >>>> (or all?), however, do not allow the voltage to go below 1.0V. Thus, raise the >>>> voltage for the lowest operating point to 1.0V so all boards can actually use >>>> it. >>> >>> Surely it wouldn't be added here if some could supply 0.9v. >> >> On the side, the original OPPs in the FEX files are actually >> frequency/voltage ranges, and not just points. Mainlines OPPv2 >> will support these, along with turbo frequencies. > > Ah, that makes sense. > >> Furthermore, the FEX files also have fields that limit the >> minimum and maximum frequencies. > > Is this going to be supported by OPPv2 too? IIRC yes, OPPv2 moves to a range profile. OPPv2 is not merged yet. >>> Is the code that uses this smart enough to sensibly switch between two >>> operating points with the same frequency and different voltages? If >>> so, maybe just add a 144MHz @ 1.0v operating point? >> >> You could try. Though I really don't see much to gain here. > > From what I recall, lower frequency = less power usage, though my > experience is from x86 laptops, not ARM SoCs and I'm sure I'm missing > a lot of details. This is the sort of thing that requires thorough > testing on a dev board. I agree, though my limited experiences tell me that the major savings come from lowering the core voltage. >>> (Alternatively, would it make sense to modify the code that uses this >>> to use frequencies with voltages specified that are lower than can be >>> supplied with the lowest voltage it can?) >> >> I think that's a bit harder to get accepted. > > Oh, definitely. It kinda makes sense, but at the same time it'll > require some seriously thorough testing on a lot of different boards. > > My only real objection here is are there boards that can go down to > 0.9v and if so, won't this change make them less power efficient in > the almost-idle case? And are those power savings enough to justify > not accepting this patch? This will require most testing as well. (sigh) Alas, my boards aren't stable enough at 0.9V, so I can't say much about it. ChenYu -- 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
