linux-kernel - Re: [PATCH v7 3/7] dt-bindings: iio: accel: adxl345: add interrupt-names

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Message-ID: <20241219-pregame-blot-e15ff0fbfe45@spud>
Date: Thu, 19 Dec 2024 18:21:10 +0000
From: Conor Dooley <conor@...nel.org>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Lothar Rubusch <l.rubusch@...il.com>, lars@...afoo.de,
	Michael.Hennerich@...log.com, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, devicetree@...r.kernel.org,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	eraretuya@...il.com
Subject: Re: [PATCH v7 3/7] dt-bindings: iio: accel: adxl345: add
 interrupt-names

On Thu, Dec 19, 2024 at 05:58:15PM +0000, Jonathan Cameron wrote:
> On Sun, 15 Dec 2024 14:56:58 +0000
> Conor Dooley <conor@...nel.org> wrote:
> 
> > On Sat, Dec 14, 2024 at 12:10:57PM +0000, Jonathan Cameron wrote:
> > > On Fri, 13 Dec 2024 21:19:05 +0000
> > > Lothar Rubusch <l.rubusch@...il.com> wrote:
> > >   
> > > > Add interrupt-names INT1 and INT2 for the two interrupt lines of the
> > > > sensor.
> > > > 
> > > > When one of the two interrupt lines is connected, the interrupt as its
> > > > interrupt-name, need to be declared in the devicetree. The driver then
> > > > configures the sensor to indicate its events on either INT1 or INT2.
> > > > 
> > > > If no interrupt is configured, then no interrupt-name should be
> > > > configured, and vice versa. In this case the sensor runs in FIFO BYPASS
> > > > mode. This allows sensor measurements, but none of the sensor events.
> > > > 
> > > > Signed-off-by: Lothar Rubusch <l.rubusch@...il.com>  
> > > 
> > > Just to repeat what I sent in reply to v6 (well after you'd posted this).
> > > Maybe we can maintain compatibility with the binding before this by adding
> > > a default of INT1.  
> > 
> > But can you make that assumption? If we did, and it's not universally
> > true, we break systems that had INT2 connected that previously worked.
> 
> I guess there is a possibility of a driver in some other OS assuming INT2, but
> seems an odd 'default' choice.

Ye, I think that it is unlikely a driver author would think that way.

> Also odd for a writer of DT for a platform
> to assume it.

I agree, I think it is unlikely that someone would assume it'd work like
this. I think a lack of attention paid to the schematic of the board is
a more likely culprit.

> There is a thing that comes up in spec orgs when discussing whether to
> rush out an errata.  "Is this bug something people would get wrong
> thinking the answer was clear, or something where the would ask a question?"
> Anyone who thinks INT2 is the obvious choice for me falls into the would
> ask category.
> 
> However, in the linux driver we would would go from assuming no interrupts
> to assuming the wrong one.  That's indeed bad.  So I guess this doesn't work.
> Oh well no default it is.

I don't think you really lose anything from having no default. The
driver works just fine without the interrupt, so the albeit small risk
just doesn't seem worth it.

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