Re: [PATCH v4 3/5] dt-bindings: iio: dac: Add adi,ltc2664.yaml

[Conor Dooley <conor@kernel.org>]

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On Mon, Jun 24, 2024 at 03:13:56PM +0000, Paller, Kim Seer wrote:
> 
> 
> > -----Original Message-----
> > From: Conor Dooley <conor@kernel.org>
> > Sent: Thursday, June 20, 2024 1:57 AM
> > To: Paller, Kim Seer <KimSeer.Paller@analog.com>
> > Cc: linux-kernel@vger.kernel.org; linux-iio@vger.kernel.org;
> > devicetree@vger.kernel.org; Jonathan Cameron <jic23@kernel.org>; David
> > Lechner <dlechner@baylibre.com>; Lars-Peter Clausen <lars@metafoo.de>;
> > Liam Girdwood <lgirdwood@gmail.com>; Mark Brown <broonie@kernel.org>;
> > Dimitri Fedrau <dima.fedrau@gmail.com>; Krzysztof Kozlowski
> > <krzk+dt@kernel.org>; Rob Herring <robh@kernel.org>; Conor Dooley
> > <conor+dt@kernel.org>; Hennerich, Michael
> > <Michael.Hennerich@analog.com>; Nuno Sá <noname.nuno@gmail.com>
> > Subject: Re: [PATCH v4 3/5] dt-bindings: iio: dac: Add adi,ltc2664.yaml
> > 
> > [External]
> > 
> > On Wed, Jun 19, 2024 at 02:49:02PM +0800, Kim Seer Paller wrote:
> > > Add documentation for ltc2664.
> > >
> > > Co-developed-by: Michael Hennerich <michael.hennerich@analog.com>
> > > Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
> > > Signed-off-by: Kim Seer Paller <kimseer.paller@analog.com>
> > > ---
> > >  .../bindings/iio/dac/adi,ltc2664.yaml         | 167 ++++++++++++++++++
> > >  MAINTAINERS                                   |   8 +
> > >  2 files changed, 175 insertions(+)
> > >  create mode 100644
> > > Documentation/devicetree/bindings/iio/dac/adi,ltc2664.yaml
> > >
> > > diff --git
> > > a/Documentation/devicetree/bindings/iio/dac/adi,ltc2664.yaml
> > > b/Documentation/devicetree/bindings/iio/dac/adi,ltc2664.yaml
> > > new file mode 100644
> > > index 000000000000..be37700e3b1f
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/iio/dac/adi,ltc2664.yaml
> > > @@ -0,0 +1,167 @@
> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) %YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/iio/dac/adi,ltc2664.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: Analog Devices LTC2664 DAC
> > > +
> > > +maintainers:
> > > +  - Michael Hennerich <michael.hennerich@analog.com>
> > > +  - Kim Seer Paller <kimseer.paller@analog.com>
> > > +
> > > +description: |
> > > +  Analog Devices LTC2664 4 channel, 12-/16-Bit, +-10V DAC
> > > +
> > > +https://www.analog.com/media/en/technical-documentation/data-sheets/2
> > > +664fa.pdf
> > > +
> > > +properties:
> > > +  compatible:
> > > +    enum:
> > > +      - adi,ltc2664
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  spi-max-frequency:
> > > +    maximum: 50000000
> > > +
> > > +  vcc-supply:
> > > +    description: Analog Supply Voltage Input.
> > > +
> > > +  v-pos-supply:
> > > +    description: Positive Supply Voltage Input.
> > > +
> > > +  v-neg-supply:
> > > +    description: Negative Supply Voltage Input.
> > > +
> > > +  iovcc-supply:
> > > +    description: Digital Input/Output Supply Voltage.
> > > +
> > > +  ref-supply:
> > > +    description:
> > > +      Reference Input/Output. The voltage at the REF pin sets the full-scale
> > > +      range of all channels. If not provided the internal reference is used and
> > > +      also provided on the VREF pin.
> > > +
> > > +  reset-gpios:
> > > +    description:
> > > +      Active-low Asynchronous Clear Input. A logic low at this level-triggered
> > > +      input clears the part to the reset code and range determined by the
> > > +      hardwired option chosen using the MSPAN pins. The control registers are
> > > +      cleared to zero.
> > > +    maxItems: 1
> > > +
> > > +  adi,manual-span-operation-config:
> > > +    description:
> > > +      This property must mimic the MSPAN pin configurations. By tying the
> > MSPAN
> > > +      pins (MSP2, MSP1 and MSP0) to GND and/or VCC, any output range can
> > be
> > > +      hardware-configured with different mid-scale or zero-scale reset options.
> > > +      The hardware configuration is latched during power on reset for proper
> > > +      operation.
> > > +        0 - MPS2=GND, MPS1=GND, MSP0=GND (+-10V, reset to 0V)
> > > +        1 - MPS2=GND, MPS1=GND, MSP0=VCC (+-5V, reset to 0V)
> > > +        2 - MPS2=GND, MPS1=VCC, MSP0=GND (+-2.5V, reset to 0V)
> > > +        3 - MPS2=GND, MPS1=VCC, MSP0=VCC (0V to 10, reset to 0V)
> > > +        4 - MPS2=VCC, MPS1=GND, MSP0=GND (0V to 10V, reset to 5V)
> > > +        5 - MPS2=VCC, MPS1=GND, MSP0=VCC (0V to 5V, reset to 0V)
> > > +        6 - MPS2=VCC, MPS1=VCC, MSP0=GND (0V to 5V, reset to 2.5V)
> > > +        7 - MPS2=VCC, MPS1=VCC, MSP0=VCC (0V to 5V, reset to 0V, enables
> > SoftSpan)
> > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > +    enum: [0, 1, 2, 3, 4, 5, 6, 7]
> > 
> > Can you explain why this property is required, when below there's one that sets
> > the ranges in microvolts? Isn't the only new information that this provides the
> > reset values (in a few cases that it is not 0).
> > What am I missing?
> 
> For specifying output range and reset options without relying on software initialization
> routines, and also for enabling the softspan feature, I think this property seems essential.

The portion of this information that is duplicated below I do not think
should reappear in this property.
Really the only additional information is the reset values being at 50%
of the range and the SoftSpan

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