[1/2] dt-bindings: iio: adc: ti-ads1298: Add driver

Commit Message

Mike Looijmans Dec. 13, 2023, 9:47 a.m. UTC

Skeleton driver for the TI ADS1298 medical ADC. This device is
typically used for ECG and similar measurements. Supports data
acquisition at configurable scale and sampling frequency.

Signed-off-by: Mike Looijmans <[e-mail]>

---

 .../bindings/iio/adc/ti,ads1298.yaml          | 80 +++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml

Comments

Conor Dooley Dec. 13, 2023, 4:23 p.m. UTC | #1

On Wed, Dec 13, 2023 at 10:47:21AM +0100, Mike Looijmans wrote:
> Skeleton driver for the TI ADS1298 medical ADC. This device is
> typically used for ECG and similar measurements. Supports data
> acquisition at configurable scale and sampling frequency.

I think the commit subject and body here were accidentally copy-pasted
from the driver patch. Patches for bindings should avoid talking about
drivers and focus on the harware (unless we are talking about LEDs or
motors etc)

> 
> Signed-off-by: Mike Looijmans <[e-mail]>
> 
> ---
> 
>  .../bindings/iio/adc/ti,ads1298.yaml          | 80 +++++++++++++++++++
>  1 file changed, 80 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
> new file mode 100644
> index 000000000000..7a160ba721eb
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
> @@ -0,0 +1,80 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/ti,ads1298.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Texas Instruments' ads1298 medical ADC chips
> +
> +maintainers:
> +  - Mike Looijmans <[e-mail]>
> +
> +properties:
> +  compatible:
> +    enum:
> +      - ti,ads1298
> +
> +  reg:
> +    maxItems: 1
> +
> +  spi-cpha: true
> +
> +  reset-gpios:
> +    maxItems: 1
> +
> +  avdd-supply:
> +    description:
> +      Analog power supply, voltage between AVDD and AVSS. When providing a
> +      symmetric +/- 2.5V, the regulator should report 5V.
> +
> +  vref-supply:
> +    description:
> +      Optional reference voltage. If omitted, internal reference is used,
> +      depending on analog supply this is 2.4 or 4V.

It may be worth mentioning here what the conditions for the internal
reference being 2.4 or 4 volts actually are.

> +
> +  clocks:
> +    description: Optional 2.048 MHz external source clock on CLK pin
> +    maxItems: 1
> +
> +  clock-names:
> +    const: clk

Since you have only one clock, having clock-names (especially with a
name like "clk") is pointless IMO.

Generally though, this patch looks good to me.

Cheers,
Conor.

> +  interrupts:
> +    description: Interrupt on DRDY pin, triggers on falling edge
> +    maxItems: 1
> +
> +  label: true
> +
> +required:
> +  - compatible
> +  - reg
> +  - avdd-supply
> +  - interrupts
> +
> +allOf:
> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +    #include <dt-bindings/interrupt-controller/irq.h>
> +    spi {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        adc@1 {
> +          reg = <1>;
> +          compatible = "ti,ads1298";
> +          label = "ads1298-1-ecg";
> +          avdd-supply = <&reg_iso_5v_a>;
> +          clock-names = "clk";
> +          clocks = <&clk_ads1298>;
> +          interrupt-parent = <&gpio0>;
> +          interrupts = <78 IRQ_TYPE_EDGE_FALLING>;
> +          spi-max-frequency = <20000000>;
> +          spi-cpha;
> +        };
> +    };
> +...
> -- 
> 2.34.1
> 
> 
> Met vriendelijke groet / kind regards,
> 
> Mike Looijmans
> System Expert
> 
> 
> TOPIC Embedded Products B.V.
> Materiaalweg 4, 5681 RJ Best
> The Netherlands
> 
> T: [phone]
> E: [e-mail]
> W: www.topic.nl
> 
> Please consider the environment before printing this e-mail

Jonathan Cameron Dec. 14, 2023, 10:22 a.m. UTC | #2

On Wed, 13 Dec 2023 16:23:43 +0000
Conor Dooley <[e-mail]> wrote:

> On Wed, Dec 13, 2023 at 10:47:21AM +0100, Mike Looijmans wrote:
> > Skeleton driver for the TI ADS1298 medical ADC. This device is
> > typically used for ECG and similar measurements. Supports data
> > acquisition at configurable scale and sampling frequency.  
> 
> I think the commit subject and body here were accidentally copy-pasted
> from the driver patch. Patches for bindings should avoid talking about
> drivers and focus on the harware (unless we are talking about LEDs or
> motors etc)
> 
> > 
> > Signed-off-by: Mike Looijmans <[e-mail]>
> > 
> > ---
> > 
> >  .../bindings/iio/adc/ti,ads1298.yaml          | 80 +++++++++++++++++++
> >  1 file changed, 80 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
> > new file mode 100644
> > index 000000000000..7a160ba721eb
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
> > @@ -0,0 +1,80 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/iio/adc/ti,ads1298.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Texas Instruments' ads1298 medical ADC chips
> > +
> > +maintainers:
> > +  - Mike Looijmans <[e-mail]>
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - ti,ads1298
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  spi-cpha: true
> > +
> > +  reset-gpios:
> > +    maxItems: 1
> > +
> > +  avdd-supply:
> > +    description:
> > +      Analog power supply, voltage between AVDD and AVSS. When providing a
> > +      symmetric +/- 2.5V, the regulator should report 5V.

Any precedence in tree for doing this?  I thought we had bindings that required negative
supplies to be specified separately if present - so this would need to be 2 
supplies. e.g.
https://elixir.bootlin.com/linux/v6.7-rc5/source/Documentation/devicetree/bindings/iio/adc/ti,adc12138.yaml#L37


> > +
> > +  vref-supply:
> > +    description:
> > +      Optional reference voltage. If omitted, internal reference is used,
> > +      depending on analog supply this is 2.4 or 4V.  
> 
> It may be worth mentioning here what the conditions for the internal
> reference being 2.4 or 4 volts actually are.
> 
> > +
> > +  clocks:
> > +    description: Optional 2.048 MHz external source clock on CLK pin
> > +    maxItems: 1
> > +
> > +  clock-names:
> > +    const: clk  
> 
> Since you have only one clock, having clock-names (especially with a
> name like "clk") is pointless IMO.
> 
> Generally though, this patch looks good to me.
> 
> Cheers,
> Conor.
> 
> > +  interrupts:
> > +    description: Interrupt on DRDY pin, triggers on falling edge
> > +    maxItems: 1
> > +
> > +  label: true
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - avdd-supply
> > +  - interrupts
> > +
> > +allOf:
> > +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> > +
> > +unevaluatedProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/gpio/gpio.h>
> > +    #include <dt-bindings/interrupt-controller/irq.h>
> > +    spi {
> > +        #address-cells = <1>;
> > +        #size-cells = <0>;
> > +
> > +        adc@1 {
> > +          reg = <1>;
> > +          compatible = "ti,ads1298";
> > +          label = "ads1298-1-ecg";
> > +          avdd-supply = <&reg_iso_5v_a>;
> > +          clock-names = "clk";
> > +          clocks = <&clk_ads1298>;
> > +          interrupt-parent = <&gpio0>;
> > +          interrupts = <78 IRQ_TYPE_EDGE_FALLING>;
> > +          spi-max-frequency = <20000000>;
> > +          spi-cpha;
> > +        };
> > +    };
> > +...
> > -- 
> > 2.34.1
> > 
> > 
> > Met vriendelijke groet / kind regards,
> > 
> > Mike Looijmans
> > System Expert
> > 
> > 
> > TOPIC Embedded Products B.V.
> > Materiaalweg 4, 5681 RJ Best
> > The Netherlands
> > 
> > T: [phone]
> > E: [e-mail]
> > W: www.topic.nl
> > 
> > Please consider the environment before printing this e-mail  
>

Jonathan Cameron Dec. 14, 2023, 11:11 a.m. UTC | #3

On Wed, 13 Dec 2023 10:47:21 +0100
Mike Looijmans <[e-mail]> wrote:

> Skeleton driver for the TI ADS1298 medical ADC. This device is
> typically used for ECG and similar measurements. Supports data
> acquisition at configurable scale and sampling frequency.
> 
> Signed-off-by: Mike Looijmans <[e-mail]>
> 
> ---
> 
>  .../bindings/iio/adc/ti,ads1298.yaml          | 80 +++++++++++++++++++
>  1 file changed, 80 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
> new file mode 100644
> index 000000000000..7a160ba721eb
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
> @@ -0,0 +1,80 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/ti,ads1298.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Texas Instruments' ads1298 medical ADC chips
> +
> +maintainers:
> +  - Mike Looijmans <[e-mail]>
> +
> +properties:
> +  compatible:
> +    enum:
> +      - ti,ads1298
> +
> +  reg:
> +    maxItems: 1
> +
> +  spi-cpha: true
> +
> +  reset-gpios:
> +    maxItems: 1
> +
> +  avdd-supply:
> +    description:
> +      Analog power supply, voltage between AVDD and AVSS. When providing a
> +      symmetric +/- 2.5V, the regulator should report 5V.
Commented on in other thread.
> +
> +  vref-supply:
> +    description:
> +      Optional reference voltage. If omitted, internal reference is used,
> +      depending on analog supply this is 2.4 or 4V.
> +
There is a dvdd-supply as well.  Might be others. Makes sure to document them all.

Should probably also document the gpios as the binding should attempt to be as complete
as possible independent of what the driver currently supports.

Lots of complex options for this device and the use of those pins, so maybe something
that can be left for now - but the patch description should then mention that is intentional.

Jonathan

> +  clocks:
> +    description: Optional 2.048 MHz external source clock on CLK pin
> +    maxItems: 1
> +
> +  clock-names:
> +    const: clk
> +
> +  interrupts:
> +    description: Interrupt on DRDY pin, triggers on falling edge
> +    maxItems: 1
> +
> +  label: true
> +
> +required:
> +  - compatible
> +  - reg
> +  - avdd-supply
> +  - interrupts
> +
> +allOf:
> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> +
> +unevaluatedProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +    #include <dt-bindings/interrupt-controller/irq.h>
> +    spi {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        adc@1 {
> +          reg = <1>;
> +          compatible = "ti,ads1298";
> +          label = "ads1298-1-ecg";
> +          avdd-supply = <&reg_iso_5v_a>;
> +          clock-names = "clk";
> +          clocks = <&clk_ads1298>;
> +          interrupt-parent = <&gpio0>;
> +          interrupts = <78 IRQ_TYPE_EDGE_FALLING>;
> +          spi-max-frequency = <20000000>;
> +          spi-cpha;
> +        };
> +    };
> +...

Mike Looijmans Dec. 20, 2023, 10:42 a.m. UTC | #4

See below.


Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


TOPIC Embedded Products B.V.
Materiaalweg 4, 5681 RJ Best
The Netherlands

T: [phone]
E: [e-mail]
W: www.topic.nl

Please consider the environment before printing this e-mail
On 14-12-2023 11:22, Jonathan Cameron wrote:
> On Wed, 13 Dec 2023 16:23:43 +0000
> Conor Dooley <[e-mail]> wrote:
> 
>> On Wed, Dec 13, 2023 at 10:47:21AM +0100, Mike Looijmans wrote:
>>> Skeleton driver for the TI ADS1298 medical ADC. This device is
>>> typically used for ECG and similar measurements. Supports data
>>> acquisition at configurable scale and sampling frequency.
>>
>> I think the commit subject and body here were accidentally copy-pasted
>> from the driver patch. Patches for bindings should avoid talking about
>> drivers and focus on the harware (unless we are talking about LEDs or
>> motors etc)

Yeah, that's what happened. Will fix in next version.

>>
>>>
>>> Signed-off-by: Mike Looijmans <[e-mail]>
>>>
>>> ---
>>>
>>>   .../bindings/iio/adc/ti,ads1298.yaml          | 80 +++++++++++++++++++
>>>   1 file changed, 80 insertions(+)
>>>   create mode 100644 Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
>>> new file mode 100644
>>> index 000000000000..7a160ba721eb
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
>>> @@ -0,0 +1,80 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/iio/adc/ti,ads1298.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: Texas Instruments' ads1298 medical ADC chips
>>> +
>>> +maintainers:
>>> +  - Mike Looijmans <[e-mail]>
>>> +
>>> +properties:
>>> +  compatible:
>>> +    enum:
>>> +      - ti,ads1298
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  spi-cpha: true
>>> +
>>> +  reset-gpios:
>>> +    maxItems: 1
>>> +
>>> +  avdd-supply:
>>> +    description:
>>> +      Analog power supply, voltage between AVDD and AVSS. When providing a
>>> +      symmetric +/- 2.5V, the regulator should report 5V.
> 
> Any precedence in tree for doing this?  I thought we had bindings that required negative
> supplies to be specified separately if present - so this would need to be 2
> supplies. e.g.
> https://elixir.bootlin.com/linux/v6.7-rc5/source/Documentation/devicetree/bindings/iio/adc/ti,adc12138.yaml#L37
> 

Given that some serious thought...

Splitting into positive and negative supplies would make sense if the chip 
would have terminals for positive, negative and ground. Which it does not 
have, there's only positive and negative (which the datasheet misleadingly 
calls "analog ground").

The analog voltage supplied to the chip has no effect on its outputs, the 
analog supply must be connected between the AVDD and AVSS pins. Its relation 
to analog ground is not relevant, so whether the voltages are +5/0 or 
+2.5/-2.5 or +4/-1 or whatever does not affect the output of the ADC, which 
only reports the difference between its "p" and "n" input signals. It only 
affects the range of the inputs, as it cannot measure (p or n) outside the 
analog supply.


> 
>>> +
>>> +  vref-supply:
>>> +    description:
>>> +      Optional reference voltage. If omitted, internal reference is used,
>>> +      depending on analog supply this is 2.4 or 4V.
>>
>> It may be worth mentioning here what the conditions for the internal
>> reference being 2.4 or 4 volts actually are.

Will do (there's a 4.4 V treshold).


>>
>>> +
>>> +  clocks:
>>> +    description: Optional 2.048 MHz external source clock on CLK pin
>>> +    maxItems: 1
>>> +
>>> +  clock-names:
>>> +    const: clk
>>
>> Since you have only one clock, having clock-names (especially with a
>> name like "clk") is pointless IMO.

True.

>>
>> Generally though, this patch looks good to me.
>>
>> Cheers,
>> Conor.
>>
>>> +  interrupts:
>>> +    description: Interrupt on DRDY pin, triggers on falling edge
>>> +    maxItems: 1
>>> +
>>> +  label: true
>>> +
>>> +required:
>>> +  - compatible
>>> +  - reg
>>> +  - avdd-supply
>>> +  - interrupts
>>> +
>>> +allOf:
>>> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
>>> +
>>> +unevaluatedProperties: false
>>> +
>>> +examples:
>>> +  - |
>>> +    #include <dt-bindings/gpio/gpio.h>
>>> +    #include <dt-bindings/interrupt-controller/irq.h>
>>> +    spi {
>>> +        #address-cells = <1>;
>>> +        #size-cells = <0>;
>>> +
>>> +        adc@1 {
>>> +          reg = <1>;
>>> +          compatible = "ti,ads1298";
>>> +          label = "ads1298-1-ecg";
>>> +          avdd-supply = <&reg_iso_5v_a>;
>>> +          clock-names = "clk";
>>> +          clocks = <&clk_ads1298>;
>>> +          interrupt-parent = <&gpio0>;
>>> +          interrupts = <78 IRQ_TYPE_EDGE_FALLING>;
>>> +          spi-max-frequency = <20000000>;
>>> +          spi-cpha;
>>> +        };
>>> +    };
>>> +...
>>> -- 
>>> 2.34.1
>>>
>>>
>>> Met vriendelijke groet / kind regards,
>>>
>>> Mike Looijmans
>>> System Expert
>>>
>>>
>>> TOPIC Embedded Products B.V.
>>> Materiaalweg 4, 5681 RJ Best
>>> The Netherlands
>>>
>>> T: [phone]
>>> E: [e-mail]
>>> W: www.topic.nl
>>>
>>> Please consider the environment before printing this e-mail
>>
>

Mike Looijmans Dec. 20, 2023, 10:58 a.m. UTC | #5

Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


TOPIC Embedded Products B.V.
Materiaalweg 4, 5681 RJ Best
The Netherlands

T: [phone]
E: [e-mail]
W: www.topic.nl

Please consider the environment before printing this e-mail
On 14-12-2023 12:11, Jonathan Cameron wrote:
> On Wed, 13 Dec 2023 10:47:21 +0100
> Mike Looijmans <[e-mail]> wrote:
> 
>> Skeleton driver for the TI ADS1298 medical ADC. This device is
>> typically used for ECG and similar measurements. Supports data
>> acquisition at configurable scale and sampling frequency.
>>
>> Signed-off-by: Mike Looijmans <[e-mail]>
>>
>> ---
>>
>>   .../bindings/iio/adc/ti,ads1298.yaml          | 80 +++++++++++++++++++
>>   1 file changed, 80 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
>> new file mode 100644
>> index 000000000000..7a160ba721eb
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
>> @@ -0,0 +1,80 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/iio/adc/ti,ads1298.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Texas Instruments' ads1298 medical ADC chips
>> +
>> +maintainers:
>> +  - Mike Looijmans <[e-mail]>
>> +
>> +properties:
>> +  compatible:
>> +    enum:
>> +      - ti,ads1298
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  spi-cpha: true
>> +
>> +  reset-gpios:
>> +    maxItems: 1
>> +
>> +  avdd-supply:
>> +    description:
>> +      Analog power supply, voltage between AVDD and AVSS. When providing a
>> +      symmetric +/- 2.5V, the regulator should report 5V.
> Commented on in other thread.
>> +
>> +  vref-supply:
>> +    description:
>> +      Optional reference voltage. If omitted, internal reference is used,
>> +      depending on analog supply this is 2.4 or 4V.
>> +
> There is a dvdd-supply as well.  Might be others. Makes sure to document them all.

Extra supplies make sense, I'll add them.

> 
> Should probably also document the gpios as the binding should attempt to be as complete
> as possible independent of what the driver currently supports.
> 
> Lots of complex options for this device and the use of those pins, so maybe something
> that can be left for now - but the patch description should then mention that is intentional.

The device has so many options for connecting stuff... It's indeed possible to 
(also) use it as a GPIO expander and as a clock source and more...

I'll put it in the patch description that the definition is incomplete by design.

The main reason I'm submitting is that this is about the third time I've 
written a driver for this chip, and I'm sure that other companies are writing 
their own as well. I'm hoping this will result in some joint effort to 
properly support it...


> 
> Jonathan
> 
>> +  clocks:
>> +    description: Optional 2.048 MHz external source clock on CLK pin
>> +    maxItems: 1
>> +
>> +  clock-names:
>> +    const: clk
>> +
>> +  interrupts:
>> +    description: Interrupt on DRDY pin, triggers on falling edge
>> +    maxItems: 1
>> +
>> +  label: true
>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - avdd-supply
>> +  - interrupts
>> +
>> +allOf:
>> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
>> +
>> +unevaluatedProperties: false
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/gpio/gpio.h>
>> +    #include <dt-bindings/interrupt-controller/irq.h>
>> +    spi {
>> +        #address-cells = <1>;
>> +        #size-cells = <0>;
>> +
>> +        adc@1 {
>> +          reg = <1>;
>> +          compatible = "ti,ads1298";
>> +          label = "ads1298-1-ecg";
>> +          avdd-supply = <&reg_iso_5v_a>;
>> +          clock-names = "clk";
>> +          clocks = <&clk_ads1298>;
>> +          interrupt-parent = <&gpio0>;
>> +          interrupts = <78 IRQ_TYPE_EDGE_FALLING>;
>> +          spi-max-frequency = <20000000>;
>> +          spi-cpha;
>> +        };
>> +    };
>> +...
>

Jonathan Cameron Dec. 20, 2023, 1:59 p.m. UTC | #6

> >>> +  avdd-supply:
> >>> +    description:
> >>> +      Analog power supply, voltage between AVDD and AVSS. When providing a
> >>> +      symmetric +/- 2.5V, the regulator should report 5V.  
> > 
> > Any precedence in tree for doing this?  I thought we had bindings that required negative
> > supplies to be specified separately if present - so this would need to be 2
> > supplies. e.g.
> > https://elixir.bootlin.com/linux/v6.7-rc5/source/Documentation/devicetree/bindings/iio/adc/ti,adc12138.yaml#L37
> >   
> 
> Given that some serious thought...
> 
> Splitting into positive and negative supplies would make sense if the chip 
> would have terminals for positive, negative and ground. Which it does not 
> have, there's only positive and negative (which the datasheet misleadingly 
> calls "analog ground").
> 
> The analog voltage supplied to the chip has no effect on its outputs, the 
> analog supply must be connected between the AVDD and AVSS pins. Its relation 
> to analog ground is not relevant, so whether the voltages are +5/0 or 
> +2.5/-2.5 or +4/-1 or whatever does not affect the output of the ADC, which 
> only reports the difference between its "p" and "n" input signals. It only 
> affects the range of the inputs, as it cannot measure (p or n) outside the 
> analog supply.
> 
Ah.  Not having seen any isolators, I assumed this device was running
against a common ground with the digital side of things.
AVSS to DGND is between -3 and 0.2 so I think there is a ground even if it's
not directly connected.

Given this only operates in differential mode the fact both signals are
referenced to +-vref which is from VASS doesn't matter in the end and any
offset goes away.

So yes I think I agree.  This should be a single supply.

Jonathan

Jonathan Cameron Dec. 20, 2023, 2 p.m. UTC | #7

> > 
> > Should probably also document the gpios as the binding should attempt to be as complete
> > as possible independent of what the driver currently supports.
> > 
> > Lots of complex options for this device and the use of those pins, so maybe something
> > that can be left for now - but the patch description should then mention that is intentional.  
> 
> The device has so many options for connecting stuff... It's indeed possible to 
> (also) use it as a GPIO expander and as a clock source and more...
> 
> I'll put it in the patch description that the definition is incomplete by design.
> 
> The main reason I'm submitting is that this is about the third time I've 
> written a driver for this chip, and I'm sure that other companies are writing 
> their own as well. I'm hoping this will result in some joint effort to 
> properly support it...
> 

Fair enough. Incomplete bindings aren't ideal, but definitely better than no bindings
in my view.

Jonathan

Patch

diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
new file mode 100644
index 000000000000..7a160ba721eb
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/adc/ti,ads1298.yaml
@@ -0,0 +1,80 @@ 
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/ti,ads1298.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Texas Instruments' ads1298 medical ADC chips
+
+maintainers:
+  - Mike Looijmans <[e-mail]>
+
+properties:
+  compatible:
+    enum:
+      - ti,ads1298
+
+  reg:
+    maxItems: 1
+
+  spi-cpha: true
+
+  reset-gpios:
+    maxItems: 1
+
+  avdd-supply:
+    description:
+      Analog power supply, voltage between AVDD and AVSS. When providing a
+      symmetric +/- 2.5V, the regulator should report 5V.
+
+  vref-supply:
+    description:
+      Optional reference voltage. If omitted, internal reference is used,
+      depending on analog supply this is 2.4 or 4V.
+
+  clocks:
+    description: Optional 2.048 MHz external source clock on CLK pin
+    maxItems: 1
+
+  clock-names:
+    const: clk
+
+  interrupts:
+    description: Interrupt on DRDY pin, triggers on falling edge
+    maxItems: 1
+
+  label: true
+
+required:
+  - compatible
+  - reg
+  - avdd-supply
+  - interrupts
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@1 {
+          reg = <1>;
+          compatible = "ti,ads1298";
+          label = "ads1298-1-ecg";
+          avdd-supply = <&reg_iso_5v_a>;
+          clock-names = "clk";
+          clocks = <&clk_ads1298>;
+          interrupt-parent = <&gpio0>;
+          interrupts = <78 IRQ_TYPE_EDGE_FALLING>;
+          spi-max-frequency = <20000000>;
+          spi-cpha;
+        };
+    };
+...