RE: [PATCH] iio: ad5770r: make devicetree property reading consistent

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> -----Original Message-----
> From: Rob Herring <robh+dt@xxxxxxxxxx>
> Sent: Monday, August 16, 2021 2:19 PM
> To: Sa, Nuno <Nuno.Sa@xxxxxxxxxx>
> Cc: Jonathan Cameron <jic23@xxxxxxxxxx>; Andy Shevchenko
> <andy.shevchenko@xxxxxxxxx>; linux-iio <linux-iio@xxxxxxxxxxxxxxx>;
> Hennerich, Michael <Michael.Hennerich@xxxxxxxxxx>; Lars-Peter
> Clausen <lars@xxxxxxxxxx>
> Subject: Re: [PATCH] iio: ad5770r: make devicetree property reading
> consistent
> 
> On Mon, Aug 16, 2021 at 2:54 AM Sa, Nuno <Nuno.Sa@xxxxxxxxxx>
> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Jonathan Cameron <jic23@xxxxxxxxxx>
> > > Sent: Saturday, August 14, 2021 6:04 PM
> > > To: Sa, Nuno <Nuno.Sa@xxxxxxxxxx>
> > > Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>; Rob
> Herring
> > > <robh+dt@xxxxxxxxxx>; linux-iio <linux-iio@xxxxxxxxxxxxxxx>;
> > > Hennerich, Michael <Michael.Hennerich@xxxxxxxxxx>; Lars-Peter
> > > Clausen <lars@xxxxxxxxxx>
> > > Subject: Re: [PATCH] iio: ad5770r: make devicetree property
> reading
> > > consistent
> > >
> > > [External]
> > >
> > > On Fri, 13 Aug 2021 10:05:17 +0000
> > > "Sa, Nuno" <Nuno.Sa@xxxxxxxxxx> wrote:
> > >
> > > > > -----Original Message-----
> > > > > From: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> > > > > Sent: Friday, August 13, 2021 10:05 AM
> > > > > To: Sa, Nuno <Nuno.Sa@xxxxxxxxxx>
> > > > > Cc: Rob Herring <robh+dt@xxxxxxxxxx>; linux-iio <linux-
> > > > > iio@xxxxxxxxxxxxxxx>; Jonathan Cameron <jic23@xxxxxxxxxx>;
> > > > > Hennerich, Michael <Michael.Hennerich@xxxxxxxxxx>; Lars-
> Peter
> > > > > Clausen <lars@xxxxxxxxxx>
> > > > > Subject: Re: [PATCH] iio: ad5770r: make devicetree property
> > > reading
> > > > > consistent
> > > > >
> > > > > On Fri, Aug 13, 2021 at 10:47 AM Sa, Nuno
> <Nuno.Sa@xxxxxxxxxx>
> > > > > wrote:
> > > > > > > From: Rob Herring <robh+dt@xxxxxxxxxx>
> > > > > > > Sent: Thursday, August 12, 2021 5:11 PM
> > > > > > > On Thu, Aug 12, 2021 at 3:14 AM Sa, Nuno
> > > <Nuno.Sa@xxxxxxxxxx>
> > > > > > > wrote:
> > > > >
> > > > > ...
> > > > >
> > > > > > > > Could you give your input on this one?
> > > > > > >
> > > > > > > There's no context, but I'm assuming this is in channel
> nodes.
> > > Keep
> > > > > >
> > > > > > Sorry about that. Your assumption is correct, the binding is for
> a
> > > > > channel
> > > > > > node [1]. The driver just get's it as 'num' [2] which is not
> > > consistent.
> > > > > > Naively, I just though changing the driver to use reg would be
> > > > > enough
> > > > > > but Andy nicely raised the question of someone being already
> > > relying
> > > > > > on 'num'...
> > > > > >
> > > > > > > the binding 'reg' and make the driver support both if
> needed.
> > > > > > > Considering the author of the binding also changed the
> binding
> > > > > from
> > > > > > > num to reg shortly after adding the binding, I don't think
> 'num'
> > > > > > > support is needed. If someone used 'num' and didn't run
> > > > > validation,
> > > > > > > well, that's their problem.
> > > > > > >
> > > > > >
> > > > > > So I guess the solution here is just to change the driver to
> support
> > > > > both
> > > > > > reg and num.
> > > > >
> > > > > As far as I got Rob's answer, if the binding never had the 'num',
> > > > > dropping it from the driver is what we want now (actually your
> > > > > original patch) and users, who are 'too much clever' :-) should
> have
> > > > > had run validation for their DTs before production.
> > > > >
> > > > > Taking this into account, I'm fine with the patch (but update a
> > > commit
> > > > > message to summarize this discussion)
> > > > > Reviewed-by: Andy Shevchenko
> <andy.shevchenko@xxxxxxxxx>
> > > > >
> > > >
> > > > You're right...
> > > > Jonathan, do you want a v2 with an updated commit message?
> > >
> > > Please do. Also please add a fixes tag given we are treating it
> > > as a fix.  If we discover someone is using the num variant then
> > > we'll just have to support both values as a fix to the fix.
> > > Not ideal, but as observed, hopefully people are validating the
> > > DTs (which basically means no one is using this in production or
> > > it would have been pointed out before).
> > >
> >
> > Well, It seems we need to go through the support both 'num' and
> 'reg'
> > route... I did some git blaming and it turns out 'num' was actually
> supported
> > in the bindings [1]. After some time it was replaced by 'reg' [2]
> leaving the
> > driver unchanged... I guess we have a significant window of time
> here
> > where someone could deploy a *validated* devicetree using 'num'...
> 
> No there wasn't. Both commits landed in v5.7.

Ahh I see. I just looked to dates without thinking in release cycles...

> > If no objections, on v2 I will just try to get 'reg' and if not present,
> fallback
> > to 'num' before erroring out.
> 
> Unless a user turns up and complains, then I say drop 'num'.
> 

Ok, thanks! That's easier for me...

- Nuno Sá




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