Re: [PATCH 3/4] arm64: dts: mediatek: mt6360: add PMIC MT6360 related nodes

[Chen-Yu Tsai]

On Mon, Aug 28, 2023 at 5:59 PM Macpaul Lin <macpaul.lin@xxxxxxxxxxxx> wrote:
>
>
> On 8/28/23 12:36, Chen-Yu Tsai wrote:
> >
> >
> > External email : Please do not click links or open attachments until you
> > have verified the sender or the content.
> >
> > On Fri, Aug 25, 2023 at 7:46 PM Macpaul Lin <macpaul.lin@xxxxxxxxxxxx> wrote:
> >>
> >> MT6360 is the secondary PMIC for MT8195.
> >> It supports USB Type-C and PD functions.
> >> Add MT6360 related common nodes which is used for MT8195 platform, includes
> >>  - charger
> >>  - ADC
> >>  - LED
> >>  - regulators
> >>
> >> Signed-off-by: Macpaul Lin <macpaul.lin@xxxxxxxxxxxx>
> >> ---
> >>  arch/arm64/boot/dts/mediatek/mt6360.dtsi | 112 +++++++++++++++++++++++
>
> [snip..]
>
> >> +       regulator {
> >> +               compatible = "mediatek,mt6360-regulator";
> >> +               LDO_VIN3-supply = <&mt6360_buck2>;
> >> +
> >> +               mt6360_buck1: buck1 {
> >> +                       regulator-compatible = "BUCK1";
> >> +                       regulator-name = "mt6360,buck1";
> >
> > Normally there's no need to provide a default name. Any used regulator
> > should have been named to match the power rail name from the board's
> > schematics.
> >
>
> I have 2 schematics on hand. One is mt8195-demo board and the other is
> genio-1200-evk board. There are 2 PMIC used on these board
> with "the same" sub power rail name for "BUCK1~BUCK4". One is mt6315,
> and the other is mt6360.

This is more of an board level integration thing. Regulator names are
expected to be named after the actual power rail names. For example,
take a look at Rock Pi 4 schematics [1], the power rail from BUCK1 of
the RK808 PMIC is named "VDD_CENTER". And in the dts file [1] we can
see the regulator is named that as well (albeit with some style changes).

Now if a project really chooses meaningless names like BUCKx or LDOy
for their power rails, then so be it. However those are board level
decisions. The names are there to help with integration debugging, so
it makes sense to have names that match the power rail names in the
schematics. Default names rarely make sense.

[1] https://dl.radxa.com/rockpi4/docs/hw/rockpi4/rockpi4_v13_sch_20181112.pdf
[2] https://elixir.bootlin.com/linux/latest/source/arch/arm64/boot/dts/rockchip/rk3399-rock-pi-4.dtsi#L267

> I've also inspected other dtsi of the regulators, such as mt6357 and
> mt6359. They have regulator nodes with named for their purpose. For the
> schematics of mt8195-demo and genio-1200-evk boards, there are no
> explicit usage for "BUCK1~BUCK4" for both mt6135 and mt6360. In order to
> specify the sub power rail for mt6360, MediaTek chooses name like
> "mt6360,buck1" instead of simple name "buck1" for distinguish with
> "buck1" of mt6351.
>
> >> +                       regulator-min-microvolt = <300000>;
> >> +                       regulator-max-microvolt = <1300000>;
> >
> > These values correspond to the regulator's range. They make no sense as
> > regulator constraints. The min/max values are supposed to be the most
> > restrictive set of voltages of the regulator consumers. If what is fed
> > by this regulator can only take 0.7V ~ 1.1V, then it should save 0.7V
> > and 1.1V here. If the regulator is unused, then there are no constraints,
> > and these can be left out.
> >
> > Just leave them out of the file.
> >
> > Both comments apply to all the regulators.
> >
> > ChenYu
>
> There are some common circuit design for these regulators like mt6359,
> mt6360 and mt6315 used on many products. MediaTek put the most common
> and expected default values in their dtsi. However, some changes still
> need to be applied to derivative boards according to product's
> requirements. The actual value be used will be applied in board's dts
> file to override the default settings in dtsi.

The values here are definitely not some product's expected values.
They are the full range of output voltages supported, as seen in the
driver.

The regulator binding says:

    regulator-min-microvolt:
      description: smallest voltage consumers may set

    regulator-max-microvolt:
      description: largest voltage consumers may set

The constraints given in the regulator node are those of the consumers,
not the PMIC regulator itself. As you mentioned, a board may need to
adjust the range based on its design, i.e. what the board has connected
to the regulator.

So either something is connected, and the consumer's constraints are set
by overriding the default in the board .dts file; or, nothing is connected
and the constraints don't matter, as nothing is going to set the voltage
or enable the regulator. So there's no reason to give a default. For
unused regulator outputs, their device nodes don't even have to exist.

I'm trying to get people to _not_ write default values, as they don't
make any sense. The full voltage range is already implied by the
compatible string.

ChenYu

> The regulator node "mt6360,ldo6" is not used by mt8195-demo and
> genio-1200-evk. I'll remove it in the next version.
> Thanks for the review.
>
> >> +                       regulator-allowed-modes = <MT6360_OPMODE_NORMAL
> >> +                                                  MT6360_OPMODE_LP
> >> +                                                  MT6360_OPMODE_ULP>;
> >> +               };
> >> +
> >> +               mt6360_buck2: buck2 {
> >> +                       regulator-compatible = "BUCK2";
> >> +                       regulator-name = "mt6360,buck2";
> >> +                       regulator-min-microvolt = <300000>;
> >> +                       regulator-max-microvolt = <1300000>;
> >> +                       regulator-allowed-modes = <MT6360_OPMODE_NORMAL
> >> +                                                  MT6360_OPMODE_LP
> >> +                                                  MT6360_OPMODE_ULP>;
> >> +               };
> >> +
> >> +               mt6360_ldo1: ldo1 {
> >> +                       regulator-compatible = "LDO1";
> >> +                       regulator-name = "mt6360,ldo1";
> >> +                       regulator-min-microvolt = <1200000>;
> >> +                       regulator-max-microvolt = <3600000>;
> >> +                       regulator-allowed-modes = <MT6360_OPMODE_NORMAL
> >> +                                                  MT6360_OPMODE_LP>;
> >> +               };
> >> +
> >> +               mt6360_ldo2: ldo2 {
> >> +                       regulator-compatible = "LDO2";
> >> +                       regulator-name = "mt6360,ldo2";
> >> +                       regulator-min-microvolt = <1200000>;
> >> +                       regulator-max-microvolt = <3600000>;
> >> +                       regulator-allowed-modes = <MT6360_OPMODE_NORMAL
> >> +                                                  MT6360_OPMODE_LP>;
> >> +               };
> >> +
> >> +               mt6360_ldo3: ldo3 {
> >> +                       regulator-compatible = "LDO3";
> >> +                       regulator-name = "mt6360,ldo3";
> >> +                       regulator-min-microvolt = <1200000>;
> >> +                       regulator-max-microvolt = <3600000>;
> >> +                       regulator-allowed-modes = <MT6360_OPMODE_NORMAL
> >> +                                                  MT6360_OPMODE_LP>;
> >> +               };
> >> +
> >> +               mt6360_ldo5: ldo5 {
> >> +                       regulator-compatible = "LDO5";
> >> +                       regulator-name = "mt6360,ldo5";
> >> +                       regulator-min-microvolt = <2700000>;
> >> +                       regulator-max-microvolt = <3600000>;
> >> +                       regulator-allowed-modes = <MT6360_OPMODE_NORMAL
> >> +                                                  MT6360_OPMODE_LP>;
> >> +               };
> >> +
> >> +               mt6360_ldo6: ldo6 {
> >> +                       regulator-compatible = "LDO6";
> >> +                       regulator-name = "mt6360,ldo6";
> >> +                       regulator-min-microvolt = <500000>;
> >> +                       regulator-max-microvolt = <2100000>;
> >> +                       regulator-allowed-modes = <MT6360_OPMODE_NORMAL
> >> +                                                  MT6360_OPMODE_LP>;
> >> +               };
> >> +
> >> +               mt6360_ldo7: ldo7 {
> >> +                       regulator-compatible = "LDO7";
> >> +                       regulator-name = "mt6360,ldo7";
> >> +                       regulator-min-microvolt = <500000>;
> >> +                       regulator-max-microvolt = <2100000>;
> >> +                       regulator-allowed-modes = <MT6360_OPMODE_NORMAL
> >> +                                                  MT6360_OPMODE_LP>;
> >> +               };
> >> +       };
> >> +};
> >> --
> >> 2.18.0
> >>
>
> Best regards,
> Macpaul Lin.