linux-kernel - Re: [PATCH 3/3] dt-bindings: iio: dac: fix ad3552r gain parameter names

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Date: Mon, 13 May 2024 14:03:35 -0500
From: David Lechner <dlechner@...libre.com>
To: Rob Herring <robh@...nel.org>
Cc: Angelo Dureghello <adureghello@...libre.com>, jic23@...nel.org, krzk+dt@...nel.org, 
	conor+dt@...nel.org, nuno.sa@...log.com, lars@...afoo.de, 
	Michael.Hennerich@...log.com, linux-iio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] dt-bindings: iio: dac: fix ad3552r gain parameter names

On Mon, May 13, 2024 at 1:52 PM Rob Herring <robh@...nel.org> wrote:
>
> On Fri, May 10, 2024 at 10:43:18AM -0500, David Lechner wrote:
> > On Fri, May 10, 2024 at 9:19 AM Angelo Dureghello
> > <adureghello@...libre.com> wrote:
> > >
> > > From: Angelo Dureghello <adureghello@...libre.com>
> > >
> > > The adi,gain-scaling-p/n values are an inverted log2,
> > > so initial naiming was set correct, but the driver uses just
> > > adi,gain-scaling-p/n, so uniforming documentation, that seems
> > > a less-risk fix for future rebases, and still conformant to datasheet.
> > >
> > > Signed-off-by: Angelo Dureghello <adureghello@...libre.com>
> > > ---
> > >  .../devicetree/bindings/iio/dac/adi,ad3552r.yaml | 16 ++++++++--------
> > >  1 file changed, 8 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml b/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml
> > > index 17442cdfbe27..9e3dbf890bfa 100644
> > > --- a/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml
> > > +++ b/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml
> > > @@ -94,13 +94,13 @@ patternProperties:
> > >              maximum: 511
> > >              minimum: -511
> > >
> > > -          adi,gain-scaling-p-inv-log2:
> > > -            description: GainP = 1 / ( 2 ^ adi,gain-scaling-p-inv-log2)
> > > +          adi,gain-scaling-p:
> > > +            description: GainP = 1 / ( 2 ^ adi,gain-scaling-p)
> > >              $ref: /schemas/types.yaml#/definitions/uint32
> > >              enum: [0, 1, 2, 3]
> > >
> > > -          adi,gain-scaling-n-inv-log2:
> > > -            description: GainN = 1 / ( 2 ^ adi,gain-scaling-n-inv-log2)
> > > +          adi,gain-scaling-n:
> > > +            description: GainN = 1 / ( 2 ^ adi,gain-scaling-n)
> > >              $ref: /schemas/types.yaml#/definitions/uint32
> > >              enum: [0, 1, 2, 3]
> > >
> > > @@ -109,8 +109,8 @@ patternProperties:
> > >
> > >          required:
> > >            - adi,gain-offset
> > > -          - adi,gain-scaling-p-inv-log2
> > > -          - adi,gain-scaling-n-inv-log2
> > > +          - adi,gain-scaling-p
> > > +          - adi,gain-scaling-n
> > >            - adi,rfb-ohms
> > >
> > >      required:
> > > @@ -214,8 +214,8 @@ examples:
> > >                  reg = <1>;
> > >                  custom-output-range-config {
> > >                      adi,gain-offset = <5>;
> > > -                    adi,gain-scaling-p-inv-log2 = <1>;
> > > -                    adi,gain-scaling-n-inv-log2 = <2>;
> > > +                    adi,gain-scaling-p = <1>;
> > > +                    adi,gain-scaling-n = <2>;
> > >                      adi,rfb-ohms = <1>;
> > >                  };
> > >              };
> > > --
> > > 2.45.0.rc1
> > >
> > >
> >
> > The DT bindings are generally considered immutable. So unless we can
> > prove that no one has ever put adi,gain-scaling-n-inv-log2 in a .dtb
> > file,
>
> You can't ever prove that.
>
> > we probably need to fix this in the driver rather than in the
> > bindings. (The driver can still handle adi,gain-scaling-p in the
> > driver for backwards compatibility but the official binding should be
> > what was already accepted in the .yaml file)
>
> If we can reasonable assume that the Linux driver is the only consumer,
> there are no upstream dts users (in kernel or other opensource
> projects), and/or the property is somewhat recent, then that's good
> enough IMO.
>
> Rob

Ack. I stand corrected then.