linux-kernel - RE: [PATCH 3/4] dt-bindings: i3c: Make 'assigned-address' valid if static address != 0

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Date:   Thu, 29 Aug 2019 14:06:00 +0000
From:   Vitor Soares <Vitor.Soares@...opsys.com>
To:     Boris Brezillon <boris.brezillon@...labora.com>,
        Vitor Soares <Vitor.Soares@...opsys.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-i3c@...ts.infradead.org" <linux-i3c@...ts.infradead.org>,
        "bbrezillon@...nel.org" <bbrezillon@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>
Subject: RE: [PATCH 3/4] dt-bindings: i3c: Make 'assigned-address' valid if
 static address != 0

Hi Boris,

From: Boris Brezillon <boris.brezillon@...labora.com>
Date: Thu, Aug 29, 2019 at 11:51:38

> On Thu, 29 Aug 2019 12:19:34 +0200
> Vitor Soares <Vitor.Soares@...opsys.com> wrote:
> 
> > The I3C devices without a static address can require a specific dynamic
> > address for priority reasons.
> > 
> > Let's update the binding document to make the 'assigned-address' property
> > valid if static address != 0 and add an example with this use case.
> 
>            ^ you mean static address == 0, right?

Indeed.

> 
> Yes, it makes sense to support that case and do our best to assign the
> requested address after DAA has taken place by explicitly executing
> SETDA.
> 
> > 
> > Signed-off-by: Vitor Soares <vitor.soares@...opsys.com>
> > ---
> >  Documentation/devicetree/bindings/i3c/i3c.txt | 13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/i3c/i3c.txt b/Documentation/devicetree/bindings/i3c/i3c.txt
> > index ab729a0..c851e75 100644
> > --- a/Documentation/devicetree/bindings/i3c/i3c.txt
> > +++ b/Documentation/devicetree/bindings/i3c/i3c.txt
> > @@ -98,9 +98,7 @@ Required properties
> >  
> >  Optional properties
> >  -------------------
> > -- assigned-address: dynamic address to be assigned to this device. This
> > -		    property is only valid if the I3C device has a static
> > -		    address (first cell of the reg property != 0).
> > +- assigned-address: dynamic address to be assigned to this device.
> 
> We should probably mention that we don't provide strong guarantees
> here. We will try to assign this dynamic address to the device, but if
> something fails (like another device owning the address and refusing to
> give it up), the actual dynamic address will be different.
> This clarification can be done in a separate patch.

So, another patch on top of this one explaining that, right?

I would suggest to use a dynamic address, like 0x40 (mid priority), on 
ENTDAA so lowers addresses (High Priority) can be used in DT or another 
method.

What do you think about this? 

> 
> >  
> >  
> >  Example:
> > @@ -129,6 +127,15 @@ Example:
> >  
> >  		/*
> >  		 * I3C device without a static I2C address but requiring
> > +		 * specific dynamic address.
> > +		 */
> > +		sensor@0,39200154004 {
> > +			reg = <0x0 0x6072 0x303904d2>;
> > +			assigned-address = <0xb>;
> > +		};
> > +
> > +		/*
> > +		 * I3C device without a static I2C address but requiring
> >  		 * resources described in the DT.
> >  		 */
> >  		sensor@0,39200154004 {

Best regards,
Vitor Soares