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

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Date:   Thu, 9 Jun 2022 11:03:32 +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 02/05/22 11:00, Aswath Govindraju wrote:
> 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.
> 

A gentle ping regarding the above question.

Thanks,
Aswath

> 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
>>>>
>>>>
>>


-- 
Thanks,
Aswath