linux-kernel - Re: [PATCH 3/4] dt-bindings: i2c-stm32: add SMBus Alert bindings

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Date:   Wed, 13 May 2020 07:42:31 +0200
From:   Alain Volmat <alain.volmat@...com>
To:     Rob Herring <robh@...nel.org>
CC:     "wsa@...nel.org" <wsa@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        Pierre Yves MORDRET <pierre-yves.mordret@...com>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Fabrice GASNIER <fabrice.gasnier@...com>
Subject: Re: [PATCH 3/4] dt-bindings: i2c-stm32: add SMBus Alert bindings

Hello Rob,

On Wed, May 13, 2020 at 02:19:32AM +0000, Rob Herring wrote:
> On Tue, May 05, 2020 at 07:51:10AM +0200, Alain Volmat wrote:
> > Add a new binding of the i2c-stm32f7 driver to enable the handling
> > of the SMBUS-Alert
> > 
> > Signed-off-by: Alain Volmat <alain.volmat@...com>
> > ---
> >  Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml b/Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml
> > index b50a2f420b36..04c0882c3661 100644
> > --- a/Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml
> > +++ b/Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml
> > @@ -36,6 +36,10 @@ allOf:
> >                  minItems: 3
> >                  maxItems: 3
> >  
> > +        st,smbus-alert:
> > +          description: Enable the SMBus Alert feature
> > +          $ref: /schemas/types.yaml#/definitions/flag
> > +
> 
> We already have smbus_alert interrupt. Can't you just check for this in 
> the slave nodes and enable if found?

My understanding reading the code (smbalert_probe within i2c-smbus.c, of_i2c_setup_smbus_alert called when
registering an adapter within i2c-core-smbus.c) is that smbus_alert refers to an interrupt on the
adapter side. That is an interrupt that would be triggered when the adapter is receiving an smbus_alert
message.
In our case (stm32f7), we do not have specific interrupt for that purpose. The interrupt triggered when
an SMBUS Alert is received (by the adapter) is the same interrupt as for other reasons and we check
within the irq handler within stm32f7 the reason before calling i2c_handle_smbus_alert if the status
register indicated an SMBUS Alert.
So my understanding is that we cannot rely on the mechanism of naming an interrupt smbus_alert.
Did I misunderstood something ?

> 
> >    - if:
> >        properties:
> >          compatible:
> > -- 
> > 2.17.1
> >