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

[Alain Volmat]

Gentle Reminder, as I wrote in my previous responce, smbus_alert interrupt
refers to an host and not a client. And since we do not have a dedicated
irq for smbus_alert, I propose to add this st, binding to enable the
smbus_alert mechanism.

On Wed, May 13, 2020 at 07:42:31AM +0200, Alain Volmat wrote:
> 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@xxxxxx>
> > > ---
> > >  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
> > >