On 11/23/2017 02:48 PM, Martin Peres wrote: > On 23/11/17 10:06, John Hubbard wrote: >> On 11/22/2017 05:07 PM, Martin Peres wrote: >>> Hey, >>> >>> Thanks for your answer, Andy! >>> >>> On 22/11/17 04:06, Ilia Mirkin wrote: >>>> On Tue, Nov 21, 2017 at 8:29 PM, Andy Ritger <arit...@nvidia.com> wrote: >>>> Martin's question was very long, but it boils down to this: >>>> >>>> How do we compute the correct values to write into the e114/e118 pwm >>>> registers based on the VBIOS contents and current state of the board >>>> (like temperature). >>> >>> Unfortunately, it can also be the e11c/e120 couple, or 0x200d8/dc on >>> GF119+, or 0x200cd/d0 on Kepler+. >>> >>> At least, it looks like we know which PWM controler we need to drive, so >>> I did not want to muddy the water even more by giving register >>> addresses, rather concentrating on the problem at hand: How to compute >>> the duty value for the PWM controler. >>> >>>> >>>> We generally do this right, but appear to get it extra-wrong for certain >>>> GPUs. >>> >>> Yes... So far, we are always safe, but users tend to mind when their >>> computer sound like a jumbo jet at take off... Who would have thought? :D >>> >>> Anyway, looking forward to your answer! >>> >>> Cheers, >>> Martin >> >> >> Hi Martin, >> >> One of our firmware engineers thinks that this looks a lot like PWM >> inversion. >> For some SKUs, the interpretation of the PWM duty cycle is inverted. That >> would probably make it *very* difficult to find a sensible algorithm that >> covered all the SKUs, given that some are inverted and others are not. >> >> For the noisy GPUs, a very useful experiment would be to try inverting it, >> like this: >> >> pwmDutyCycle = pwmPeriod - pwmDutyCycle; >> >> ...and then see if fan control starts behaving closer to how you've actually >> programmed it. >> >> Would that be easy enough to try out? It should help narrow down the >> problem at least. >> > > Hey John, > > Unfortunately, we know about PWM inversion, and one can know which mode > to use based on the GPIO entry associated to the fan (inverted). We have > had support for this in Nouveau for a long time. At the very least, this > is not the problem on my GF108. > > I am certain that the problem I am seeing is related to this vbios table > I wrote about (BIT P, offset 0x18). It is used to compute what PWM duty > I should use for both 0 and 100% of the fan speed. > > Computing the value for 0% fan speed is difficult because of > non-continuous nature of some of the functions[1], but I can always > over-approximate. However, I failed to accurately compute the duty I > need to write to get the 100% fan speed (I have cases where I greatly > over-estimate it...). > > Could you please check out the vbios table I am pointing at? I am quite > sure that your documentation will be clearer than my babbling :D
Yes. We will check on this. There has been some productive discussion internally, but it will take some more investigation. thanks, John Hubbard > > Thanks, > Martin > > [1] http://fs.mupuf.org/nvidia/fan_calib/pwm_offset.png > _______________________________________________ Nouveau mailing list Nouveau@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/nouveau