Re: [RFC PATCH v2 1/6] dt-bindings: ROHM BD96801 PMIC regulators

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 15/04/2024 08:51, Matti Vaittinen wrote:
> On 4/14/24 00:27, Krzysztof Kozlowski wrote:
>> On 12/04/2024 13:21, Matti Vaittinen wrote:
>>> ROHM BD96801 is a highly configurable automotive grade PMIC. Introduce
>>> DT bindings for the BD96801 regulators.
>>>
>>> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
>>> ---
>>> Revision history:
>>> - No changes since RFCv1
>>
>> Subject: missing "regulator" prefix, as first.
>>
>>>
>>>   .../regulator/rohm,bd96801-regulator.yaml     | 69 +++++++++++++++++++
>>>   1 file changed, 69 insertions(+)
>>>   create mode 100644 Documentation/devicetree/bindings/regulator/rohm,bd96801-regulator.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/regulator/rohm,bd96801-regulator.yaml b/Documentation/devicetree/bindings/regulator/rohm,bd96801-regulator.yaml
>>> new file mode 100644
>>> index 000000000000..4015802a3d84
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/regulator/rohm,bd96801-regulator.yaml
>>> @@ -0,0 +1,69 @@
>>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/regulator/rohm,bd96801-regulator.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: ROHM BD96801 Power Management Integrated Circuit regulators
>>> +
>>> +maintainers:
>>> +  - Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
>>> +
>>> +description: |
>>> +  This module is part of the ROHM BD96801 MFD device. For more details
>>> +  see Documentation/devicetree/bindings/mfd/rohm,bd96801-pmic.yaml.
>>> +
>>> +  The regulator controller is represented as a sub-node of the PMIC node
>>> +  on the device tree.
>>> +
>>> +  Regulator nodes should be named to BUCK_<number> and LDO_<number>.
>>> +  The valid names for BD96801 regulator nodes are
>>> +  BUCK1, BUCK2, BUCK3, BUCK4, LDO5, LDO6, LDO7
>>> +
>>> +patternProperties:
>>> +  "^LDO[5-7]$":
>>
>> lowercase
>>
>>> +    type: object
>>> +    description:
>>> +      Properties for single LDO regulator.
>>> +    $ref: regulator.yaml#
>>
>> Missing unevaluatedProperties: false
>>
>>> +
>>> +    properties:
>>> +      regulator-name:
>>> +        pattern: "^ldo[5-7]$"
>>> +        description:
>>> +          Name of the regulator. Should be "ldo5", ..., "ldo7"
>>
>> Why do you enforce the name? The name should match board schematics, not
>> regulator datasheet.
> 
> If my memory serves me right, the slightly peculiar thing with the 
> regulator core is it does matching of the regulators based on the names 
> of the nodes. There was the regulator-compatible property, but I think 
> it has been deprecated long ago.
> 
> https://elixir.bootlin.com/linux/latest/source/drivers/regulator/of_regulator.c#L380
> 
> Hence the regulators tend to have fixed names for the nodes. Unless 
> there has been some recent changes I am not aware of...

Yes, names of the nodes, but not "regulator-name" property.

> 
>>> +      rohm,initial-voltage-microvolt:
>>> +        description:
>>> +          Initial voltage for regulator. Voltage can be tuned +/-150 mV from
>>> +          this value. NOTE, This can be modified via I2C only when PMIC is in
>>> +          STBY state.
>>> +        minimum: 300000
>>> +        maximum: 3300000
>>
>> Hm, regulator min/max microvolts properties don't work for you? The
>> initial will be just middle?
> 
> I had not even thought of this!
> 
> I think this is a good idea. The problem I see is if the system where 
> the PMIC is used will need to have 'initial power level' at start-up, 
> which is near the one end of the allowed voltage area. (This because the 
> "tuning"-range is quite narrow after the initial voltage is set). Wide 
> allowed voltage range may be needed if the PMIC is reconfigured using 
> the PMIC STBY state during the runtime.
> 
> Eg, sequence would look like:
> 
> Bootup:
> PMIC STBY:
>   - initial value 'A' from DT
> => PMIC ACTIVE
>   - desired (early) voltages 'A' + 'tune'
> 
> ...
> 
> Voltage state differing more than the 'tune' needed due to some runtime 
> use-case:
> => PMIC STBY
>   - initial value 'B'
> => PMIC ACTIVE
>   - desired voltages 'B' + 'tune'
> 
> Now, if the 'A' can be 'far' from the mid point of the 'allowed 
> voltages' -range.
> 
> I have no idea how valid this use-case is though. Once again, I work for 
> a component vendor and don't get to see the forest from the trees... But 
> sure I would like to enable as many possible use-cases as, well, possible :)

Still I think min/max microvolt solves your case. The property is
board-specific and should match what is really on the board. Therefore
when writing DTS, one must properly set min/max which in this particular
meaning would choose the starting voltage.

I am also fine with this property if somehow min/max create confusion or
aren't solving the problem.


Best regards,
Krzysztof