linux-kernel - Re: [PATCH 1/2] dt-bindings: usb: tps6598x: Make the interrupts property optional

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Message-ID: <f714ee55-ef47-317d-81b9-57020dda064b@ti.com>
Date:   Mon, 2 May 2022 11:00:44 +0530
From:   Aswath Govindraju <a-govindraju@...com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Roger Quadros <rogerq@...nel.org>,
        Rob Herring <robh+dt@...nel.org>
CC:     Vignesh Raghavendra <vigneshr@...com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Hector Martin <marcan@...can.st>,
        Martin Kepplinger <martink@...teo.de>,
        "Bryan O'Donoghue" <bryan.odonoghue@...aro.org>,
        <linux-usb@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: usb: tps6598x: Make the interrupts
 property optional

Hi Rob,

On 26/04/22 12:27, Heikki Krogerus wrote:
> On Tue, Apr 26, 2022 at 09:42:31AM +0300, Roger Quadros wrote:
>> Hi,
>>
>> On 22/04/2022 08:07, Aswath Govindraju wrote:
>>> Hi Roger,
>>>
>>> On 21/04/22 00:46, Roger Quadros wrote:
>>>> Hi,
>>>>
>>>> On 18/04/2022 08:19, Aswath Govindraju wrote:
>>>>> Hi Roger,
>>>>>
>>>>> On 14/04/22 23:40, Roger Quadros wrote:
>>>>>> Hi,
>>>>>>
>>>>>> On 14/04/2022 11:31, Aswath Govindraju wrote:
>>>>>>> Support for polling has been added in the driver, which will be used by
>>>>>>> default if interrupts property is not populated. Therefore, remove
>>>>>>> interrupts and interrupt-names from the required properties and add a note
>>>>>>> under interrupts property describing the above support in driver.
>>>>>>>
>>>>>>> Suggested-by: Roger Quadros <rogerq@...nel.org>
>>>>>>
>>>>>> I did not suggest to make interrupts optional by default.
>>>>>>
>>>>>> What I suggested was that if a DT property exists to explicitly
>>>>>> indicate polling mode then interrupts are not required.
>>>>>>
>>>>>
>>>>> ohh okay, got it. However, may I know if adding a dt property to
>>>>> indicate polling for aiding the driver, is the correct approach to model it?
>>>>>
>>>>> In terms of modelling hardware, as interrupts are not connected we are
>>>>> not populating the interrupts property. Shouldn't that be all. If we are
>>>>> adding a property explicitly to indicate polling that can be used by
>>>>> driver, wouldn't that be a software aid being added in the device tree?
>>>>
>>>> The hardware (tps6598x chip) has an interrupt pin and is expected to be used
>>>> in normal case.
>>>>
>>>> Some buggy boards might have forgot to connect it. We are adding polling mode only for these buggy boards. ;)
>>>> So polling mode is an exception.
>>>>
>>>
>>> Yes as you mentioned the interrupt line is expected to connected but
>>> there could be cases where there are not enough pins on the SoC and
>>> polling is used intentionally. In these cases this would be a feature
>>> rather than a bug.
>>
>> I do not agree that this is a feature but a board defect. You can always use
>> a GPIO expander to add more GPIOs than the SoC can provide.
>>
>> Type-C events are asynchronous and polling is a waste of CPU time.
>> What will you do if system suspends and you need to wake up on Type-C
>> status change?
>> So polling mode is just an exception for the defective boards or could
>> be used for debugging.
>>
>>>
>>> Also, I feel like not adding interrupts property in the dt nodes will
>>> indicate polling. My question is why are we adding an extra property
>>> (which is being used only as an aid in the driver) when this feature can
>>> be modeled by making interrupts property optional.
>>
>> Because interrupt property was not originally optional for this driver.
>>
>> I would like to hear what Heikki has to say about this.
>>
>> Any thoughts Heikki?
> 
> I think the question is generic. How should DT describe the
> connection/lack of connection? Rob should comment on this.
> 

A gentle ping regarding this.

Thanks,
Aswath

> thanks,
> 
> 
>> cheers,
>> -roger
>>
>>>
>>> Thanks,
>>> Aswath
>>>
>>>> cheers,
>>>> -roger
>>>>
>>>>>
>>>>> Thanks,
>>>>> Aswath
>>>>>
>>>>>>> Signed-off-by: Aswath Govindraju <a-govindraju@...com>
>>>>>>> ---
>>>>>>>  Documentation/devicetree/bindings/usb/ti,tps6598x.yaml | 4 ++--
>>>>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/Documentation/devicetree/bindings/usb/ti,tps6598x.yaml b/Documentation/devicetree/bindings/usb/ti,tps6598x.yaml
>>>>>>> index a4c53b1f1af3..1c4b8c6233e5 100644
>>>>>>> --- a/Documentation/devicetree/bindings/usb/ti,tps6598x.yaml
>>>>>>> +++ b/Documentation/devicetree/bindings/usb/ti,tps6598x.yaml
>>>>>>> @@ -25,6 +25,8 @@ properties:
>>>>>>>  
>>>>>>>    interrupts:
>>>>>>>      maxItems: 1
>>>>>>> +    description:
>>>>>>> +      If interrupts are not populated then by default polling will be used.
>>>>>>>  
>>>>>>>    interrupt-names:
>>>>>>>      items:
>>>>>>> @@ -33,8 +35,6 @@ properties:
>>>>>>>  required:
>>>>>>>    - compatible
>>>>>>>    - reg
>>>>>>> -  - interrupts
>>>>>>> -  - interrupt-names
>>>>>>>  
>>>>>>>  additionalProperties: true
>>>>>>>  
>>>>>>
>>>>>> cheers,
>>>>>> -roger
>>>
>>>
>