linux-kernel - Re: [PATCH v1 1/4] dt-bindings: mfd: Add DT bindings for TI TPS6594 PMIC

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Message-ID: <633753f7-2b8a-15bb-ba55-1c5a6f2eb3f1@baylibre.com>
Date:   Tue, 21 Feb 2023 16:18:30 +0100
From:   Julien Panis <jpanis@...libre.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        lee@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, corbet@....net
Cc:     hdegoede@...hat.com, eric.auger@...hat.com, jgg@...pe.ca,
        razor@...ckwall.org, suma.hegde@....com,
        stephen@...workplumber.org, arnd@...db.de,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, eblanc@...libre.com,
        jneanne@...libre.com
Subject: Re: [PATCH v1 1/4] dt-bindings: mfd: Add DT bindings for TI TPS6594
 PMIC



On 2/21/23 16:01, Krzysztof Kozlowski wrote:
> On 21/02/2023 15:49, Julien Panis wrote:
>>
>> On 2/21/23 12:17, Krzysztof Kozlowski wrote:
>>> On 17/02/2023 13:10, Julien Panis wrote:
>>>> On 2/17/23 10:06, Krzysztof Kozlowski wrote:
>>>>> On 16/02/2023 12:44, Julien Panis wrote:
>>>>>> TPS6594 is a Power Management IC which provides regulators and others
>>>>> Subject: drop second/last, redundant "DT bindings for". The
>>>>> "dt-bindings" prefix is already stating that these are bindings.
>>>>>
>>>>>
>>>>>> features like GPIOs, RTC, watchdog, ESMs (Error Signal Monitor), and
>>>>>> PFSM (Pre-configurable Finite State Machine) managing the state of the
>>>>>> device.
>>>>>> TPS6594 is the super-set device while TPS6593 and LP8764X are derivatives.
>>>>>>
>>>>>> Signed-off-by: Julien Panis <jpanis@...libre.com>
>>>>>> ---
>>>>>>     .../devicetree/bindings/mfd/ti,tps6594.yaml   | 164 ++++++++++++++++++
>>>>>>     1 file changed, 164 insertions(+)
>>>>>>     create mode 100644 Documentation/devicetree/bindings/mfd/ti,tps6594.yaml
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/mfd/ti,tps6594.yaml b/Documentation/devicetree/bindings/mfd/ti,tps6594.yaml
>>>>>> new file mode 100644
>>>>>> index 000000000000..37968d6c0420
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/devicetree/bindings/mfd/ti,tps6594.yaml
>>>>>> @@ -0,0 +1,164 @@
>>>>>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>>>>>> +%YAML 1.2
>>>>>> +---
>>>>>> +$id: http://devicetree.org/schemas/mfd/ti,tps6594.yaml#
>>>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>>>> +
>>>>>> +title: TI TPS6594 Power Management Integrated Circuit
>>>>>> +
>>>>>> +maintainers:
>>>>>> +  - Julien Panis <jpanis@...libre.com>
>>>>>> +
>>>>>> +description: |
>>>>>> +  TPS6594 is a Power Management IC which provides regulators and others
>>>>>> +  features like GPIOs, RTC, watchdog, ESMs (Error Signal Monitor), and
>>>>>> +  PFSM (Pre-configurable Finite State Machine) managing the state of the device.
>>>>>> +  TPS6594 is the super-set device while TPS6593 and LP8764X are derivatives.
>>>>>> +
>>>>>> +properties:
>>>>>> +  compatible:
>>>>>> +    enum:
>>>>>> +      - ti,tps6594
>>>>>> +      - ti,tps6593
>>>>>> +      - ti,lp8764x
>>>>> Any particular choice of ordering (different than alphabetical)?
>>>> Thank you for the review.
>>>>
>>>> I chose this ordering because it emphasizes the fact that tps6593 and
>>>> lp8764x
>>>> are derivatives of tps6594 : tps6593 is nearly the same (a minor feature
>>>> is not
>>>> supported), and lp8764x has less resources (less bucks/LDO, and no RTC).
>>>>
>>>> Besides, a multi-PMIC synchronization scheme is implemented in the PMIC
>>>> device
>>>> to synchronize the power state changes with other PMIC devices. This is done
>>>> through a SPMI bus : the master PMIC is the controller device on the
>>>> SPMI bus,
>>>> and the slave PMICs are the target devices on the SPMI bus. For the 5 boards
>>>> we work on (for which device trees will be sent in another patch series):
>>>> - tps6594 is used on 3 boards and is always master (multi-PMIC config)
>>>> - tps6593 is used on 1 board and is master (single-PMIC config)
>>>> - lp8764x is used on 2 boards and is always slave (multi-PMIC config)
>>>> There might not be situations in which lp8764x would be master and tps6594
>>>> or tps6593 would be slave.
>>>>
>>>> That's why I preferred this ordering.
>>>>
>>>> Do you think that alphabetical order would be better ?
>>> It's simpler (requires no knowledge about chips) and reduces the future
>>> conflicts. It's fine to keep it also ordered like you said, although I
>>> wonder how other people adding new compatibles here will figure it out...
>> I will reorder it alphabetically in v2.
>>
>>>>>> +
>>>>>> +  reg:
>>>>>> +    description: I2C slave address or SPI chip select number.
>>>>>> +    maxItems: 1
>>>>>> +
>>>>>> +  ti,use-crc:
>>>>>> +    type: boolean
>>>>>> +    description: If true, use CRC for I2C and SPI interface protocols.
>>>>> Hm, why different boards would like to enable or disable it? Why this
>>>>> suits DT?
>>>> You're right. Reading your comment, it appears to me that CRC feature is
>>>> not fully
>>>> related to HW description and should not be set in DT.
>>>>
>>>> CRC is not 'fully' related to HW, but...
>>>> For CRC feature as well, PMICs are synchronized (for boards with
>>>> multi-PMIC config).
>>>> To use CRC mode, this feature must be requested explicitly on the master
>>>> PMIC
>>>> through I2C or SPI driver, then it is enabled for the slave PMICs
>>>> through SPMI bus: that
>>>> sync is performed 'automatically', without intervention from the I2C or
>>>> SPI driver to
>>>> enable CRC on slave PMICs.
>>>> As a consequence, CRC feature is enabled for all PMICs at I2C/SPI driver
>>>> probe,
>>>> or it is let disabled for all PMICs. But it can't be enabled for one
>>>> PMIC and disabled
>>>> for another one.
>>>>
>>>> This will probably rediscussed for I2C/SPI drivers, but do you think
>>>> that a 'use_crc'
>>>> driver parameter would be an acceptable solution ? If so, the master
>>>> PMIC would have
>>>> to be identified, so that the driver can explicitly enable CRC mode for
>>>> this one if
>>>> 'use_crc' is true. With this solution, some 'ti,is-master;' bool
>>>> property would be necessary.
>>> It looks the property should be only in the drivers, not in the DT.
>> I will remove 'ti,use-crc;' property from the DT. This will be only in
>> the driver.
>> Do you also consider that a property such as 'ti,is-secondary-pmic;'
>> would not be acceptable either ? From driver point of view, this
>> primary/secondary role on SPMI bus is a 'built-in' property of the
>> PMIC (CRC must be enabled only via primary PMIC but using the
>> primary PMIC does not imply that CRC is necessarily used).
> Depends, I am not sure. Are the PMICs in some kind of hierarchical
> topology? Like one is parent of another? If not (so both are
> parallel/equal children of SPMI bus), then some property to indicate
> which one is the main PMIC makes sense.

There is no hierarchical topology.
So, I will consider identifying in DT which one is the main PMIC.

(...)


Julien