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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. > Do you intend to do this Matti? Otherwise I will give it a try. Kind regards, Maud