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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. Kind regards, Maud