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If I understand the comment >>>>>>>> correctly, that might allow the driver to be able to use correctly >>>>>>>> scaled voltages. >>>>>>>> >>>>>>>> https://elixir.bootlin.com/linux/v6.18-rc1/source/Documentation/ >>>>>>>> devicetree/bindings/regulator/rohm,bd71837-regulator.yaml#L108 >>>>>>> >>>>>>> Ah I didn't know those existed, should've checked the bindings in >>>>>>> more >>>>>>> detail, thanks for the hint! >>>>>>> >>>>>>> I will have to investigate this carefully, since I don't have >>>>>>> access to >>>>>>> the actual design of the COM, so I don't know exactly what is there. >>>>>> >>>>>> So I am not yet entirely sure if this works out, I used the >>>>>> calculation >>>>>> in the driver: >>>>>> >>>>>> /* >>>>>>     * Setups where regulator (especially the buck8) output voltage >>>>>> is scaled >>>>>>     * by adding external connection where some other regulator >>>>>> output is >>>>>> connected >>>>>>     * to feedback-pin (over suitable resistors) is getting popular >>>>>> amongst >>>>>> users >>>>>>     * of BD71837. (This allows for example scaling down the buck8 >>>>>> voltages >>>>>> to suit >>>>>>     * lover GPU voltages for projects where buck8 is (ab)used to >>>>>> supply power >>>>>>     * for GPU. Additionally some setups do allow DVS for buck8 but >>>>>> as this do >>>>>>     * produce voltage spikes the HW must be evaluated to be able to >>>>>> survive this >>>>>>     * - hence I keep the DVS disabled for non DVS bucks by default. I >>>>>> don't want >>>>>>     * to help you burn your proto board) >>>>>>     * >>>>>>     * So we allow describing this external connection from DT and >>>>>> scale the >>>>>>     * voltages accordingly. This is what the connection should >>>>>> look like: >>>>>>     * >>>>>>     * |------------| >>>>>>     * |    buck 8  |-------+----->Vout >>>>>>     * |        |    | >>>>>>     * |------------|    | >>>>>>     *    | FB pin    | >>>>>>     *    |        | >>>>>>     *    +-------+--R2---+ >>>>>>     *        | >>>>>>     *        R1 >>>>>>     *        | >>>>>>     *    V FB-pull-up >>>>>>     * >>>>>>     *    Here the buck output is sifted according to formula: >>>>>>     * >>>>>>     * Vout_o = Vo - (Vpu - Vo)*R2/R1 >>>>>>     * Linear_step = step_orig*(R1+R2)/R1 >>>>>>     * >>>>>>     * where: >>>>>>     * Vout_o is adjusted voltage output at vsel reg value 0 >>>>>>     * Vo is original voltage output at vsel reg value 0 >>>>>>     * Vpu is the pull-up voltage V FB-pull-up in the picture >>>>>>     * R1 and R2 are resistor values. >>>>>>     * >>>>>>     * As a real world example for buck8 and a specific GPU: >>>>>>     * VLDO = 1.6V (used as FB-pull-up) >>>>>>     * R1 = 1000ohms >>>>>>     * R2 = 150ohms >>>>>>     * VSEL 0x0 => 0.8V – (VLDO – 0.8) * R2 / R1 = 0.68V >>>>>>     * Linear Step = 10mV * (R1 + R2) / R1 = 11.5mV >>>>>>     */ >>>>>> >>>>>> Because I do not know the pull up voltage, and I am not sure if it >>>>>> is a >>>>>> pull up. >>>>>> >>>>>> So: >>>>>> Vout_o = 1.35V >>>>>> Vo = 1.1V >>>>>> Vpu = unknown >>>>>> R2 = 499 Ohm >>>>>> R1 = 2200 Ohm >>>>>> Gives: >>>>>> Vpu = ~0V >>>>>> >>>>>> And: >>>>>> Vout_o = 1.35V >>>>>> Vo = 1.1V >>>>>> Vpu = unknown >>>>>> R2 = 2200 Ohm >>>>>> R1 = 499 Ohm >>>>>> Gives: >>>>>> Vpu = ~1.04V >>>>>> >>>>>> I am not quite sure which resistor is R1 and which is R2 but having >>>>>> there be a pull down to 0V seems the most logical answer? >>>>>> >>>>>> I am adding Lothar from Ka-Ro to the CC maybe he can shed some >>>>>> light on >>>>>> this setup. >>>>> R2 is connected to GND, so Vpu = 0. >>>>> With: >>>>>     regulator-min-microvolt = <1350000>; >>>>>     regulator-max-microvolt = <1350000>; >>>>>     rohm,fb-pull-up-microvolt = <0>; >>>>>     rohm,feedback-pull-up-r1-ohms = <2200>; >>>>>     rohm,feedback-pull-up-r2-ohms = <499>; >>>>> the correct voltage should be produced on the BUCK8 output, but a >>>>> quick >>>>> test with these parameters led to: >>>>> |failed to get the current voltage: -EINVAL >>>>> |bd718xx-pmic bd71847-pmic.3.auto: error -EINVAL: failed to >>>>> register buck6 regulator >>>>> |bd718xx-pmic: probe of bd71847-pmic.3.auto failed with error -22 >>>>> >>>>> Apparently noone has ever tested this feature in real life. >>>> >>>> Thanks for trying it out Lothar. I am positive this was tested - but >>>> probably the use-case has been using a pull-up. I assume having the >>>> zero >>>> pull-up voltage causes the driver to calculate some bogus values. I >>>> think fixing the computation in the driver might not be that big of a >>>> task(?) The benefit of doing it would be that the correct voltages >>>> would >>>> be calculated by the driver. >>>> >>>> If real voltages aren't matching what is calculated by the driver, then >>>> the voltages requested by regulator consumers will cause wrong voltages >>>> to be applied. Debug interfaces will also show wrong voltages, and the >>>> safety limits set in the device-tree will not be really respected. >>>> >>>> I think this would be well worth fixing. >>>> >>> Before doing the real-life test I did the same calculation that's done >>> in the driver to be sure that it will generate the correct values: >>> bc 1.07.1 >>> Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006, 2008, 2012-2017 >>> Free Software Foundation, Inc. >>> This is free software with ABSOLUTELY NO WARRANTY. >>> For details type `warranty'. >>> fb_uv=0 >>> r1=2200 >>> r2=499 >>> min=800000 >>> step=10000 >>> # default voltage without divider >>> min+30*step >>> 1100000 >>> min=min-(fb_uv-min)*r2/r1 >>> step=step*(r1+r2)/r1 >>> min >>> 981454 >>> step >>> 12268 >>> # default voltage with divider >>> min+30*step >>> 1349494 >>> >>> Probably we need to use this value rather than the nominal 135000 as >>> the target voltage in the DTB. >> >> Yes. When the driver calculates the voltages which match the actual >> voltages, then you should also use the actual voltages in the device- >> tree. >> > > Think I've got it: > > diff --git a/drivers/regulator/bd718x7-regulator.c b/drivers/regulator/ > bd718x7-regulator.c > index 022d98f3c32a2..ea9c4058ee6a5 100644 > --- a/drivers/regulator/bd718x7-regulator.c > +++ b/drivers/regulator/bd718x7-regulator.c > @@ -1613,6 +1613,8 @@ static int setup_feedback_loop(struct device *dev, > struct device_node *np, >                                 step /= r1; > >                                 new[j].min = min; > +                               new[j].min_sel = desc- > >linear_ranges[j].min_sel; > +                               new[j].max_sel = desc- > >linear_ranges[j].max_sel; >                                 new[j].step = step; > >                                 dev_dbg(dev, "%s: old range min %d, > step %d\n", > > > the min_sel and max_sel fields were uninitialized in the new > linear_range, copying them over from the old one (they refer to the > register range if I understand correctly so they should not change) > initializes them. > > Then setting 1349494 as the actual voltage makes it fully work. > Otherwise it complains: > buck6: failed to apply 1350000-1350000uV constraint: -EINVAL > > Final debug output now: > [    0.327807] rohm-bd718x7 0-004b: buck6: old range min 800000, step 10000 > [    0.327813] rohm-bd718x7 0-004b: new range min 981454, step 12268 > [    0.327819] rohm-bd718x7 0-004b: regulator 'buck6' has FB pull-up > configured > > I will add this fix to the next version of this patchset and include > your requested change in the dts. New idea, why don't we just change the values of the original linear_range? Do away with the allocation there entirely. Kind regards, Maud