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

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Message-ID: <YmeXw8nerjpuKPC9@kuha.fi.intel.com>
Date:   Tue, 26 Apr 2022 09:57:07 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Roger Quadros <rogerq@...nel.org>
Cc:     Aswath Govindraju <a-govindraju@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.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

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.

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
> > 
> > 

-- 
heikki