Re: [PATCH 1/2] dt-bindings: iio: adc: Add binding documentation for Renesas RZ/G2L A/D converter

[Jonathan Cameron]

On Wed, 14 Jul 2021 19:24:27 +0100
"Lad, Prabhakar" <prabhakar.csengg@xxxxxxxxx> wrote:

> Hi Jonathan,
> 
> On Wed, Jul 14, 2021 at 1:39 PM Jonathan Cameron
> <Jonathan.Cameron@xxxxxxxxxx> wrote:
> >
> > On Wed, 14 Jul 2021 10:11:49 +0100
> > "Lad, Prabhakar" <prabhakar.csengg@xxxxxxxxx> wrote:
> >  
> > > Hi Jonathan,
> > >
> > > Thank you for the review.
> > >
> > > On Sat, Jul 3, 2021 at 6:17 PM Jonathan Cameron <jic23@xxxxxxxxxx> wrote:  
> > > >
> > > > On Tue, 29 Jun 2021 23:03:27 +0100
> > > > Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx> wrote:
> > > >  
> > > > > Add binding documentation for Renesas RZ/G2L A/D converter block.
> > > > >
> > > > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> > > > > Reviewed-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>  
> > > > Hi,
> > > >
> > > > See inline
> > > >
> > > > Jonathan
> > > >  
> > > > > ---
> > > > >  .../bindings/iio/adc/renesas,rzg2l-adc.yaml   | 121 ++++++++++++++++++
> > > > >  1 file changed, 121 insertions(+)
> > > > >  create mode 100644 Documentation/devicetree/bindings/iio/adc/renesas,rzg2l-adc.yaml
> > > > >
> > > > > diff --git a/Documentation/devicetree/bindings/iio/adc/renesas,rzg2l-adc.yaml b/Documentation/devicetree/bindings/iio/adc/renesas,rzg2l-adc.yaml
> > > > > new file mode 100644
> > > > > index 000000000000..db935d6d59eb
> > > > > --- /dev/null
> > > > > +++ b/Documentation/devicetree/bindings/iio/adc/renesas,rzg2l-adc.yaml
> > > > > @@ -0,0 +1,121 @@
> > > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > > +%YAML 1.2
> > > > > +---
> > > > > +$id: http://devicetree.org/schemas/iio/adc/renesas,rzg2l-adc.yaml#
> > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > +
> > > > > +title: Renesas RZ/G2L ADC
> > > > > +
> > > > > +maintainers:
> > > > > +  - Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> > > > > +
> > > > > +description: |
> > > > > +  A/D Converter block is a successive approximation analog-to-digital converter
> > > > > +  with a 12-bit accuracy. Up to eight analog input channels can be selected.
> > > > > +  Conversions can be performed in single or repeat mode. Result of the ADC is
> > > > > +  stored in a 32-bit data register corresponding to each channel.
> > > > > +
> > > > > +properties:
> > > > > +  compatible:
> > > > > +    oneOf:
> > > > > +      - items:
> > > > > +          - enum:
> > > > > +              - renesas,r9a07g044-adc   # RZ/G2{L,LC}
> > > > > +          - const: renesas,rzg2l-adc
> > > > > +
> > > > > +  reg:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  interrupts:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  clocks:
> > > > > +    items:
> > > > > +      - description: converter clock
> > > > > +      - description: peripheral clock
> > > > > +
> > > > > +  clock-names:
> > > > > +    items:
> > > > > +      - const: adclk
> > > > > +      - const: pclk
> > > > > +
> > > > > +  power-domains:
> > > > > +    maxItems: 1
> > > > > +
> > > > > +  resets:
> > > > > +    maxItems: 2
> > > > > +
> > > > > +  reset-names:
> > > > > +    items:
> > > > > +      - const: presetn
> > > > > +      - const: adrst-n
> > > > > +
> > > > > +  renesas-rzg2l,adc-trigger-mode:
> > > > > +    $ref: /schemas/types.yaml#/definitions/uint8
> > > > > +    description: Trigger mode for A/D converter
> > > > > +    enum:
> > > > > +      - 0 # Software trigger mode (Defaults)
> > > > > +      - 1 # Asynchronous trigger using ADC_TRG trigger input pin
> > > > > +      - 2 # Synchronous trigger (Trigger from MTU3a/GPT)  
> > > >
> > > > Is this a function of the board in some fashion?  If not it sounds like
> > > > something that should be in control of userspace.  Normally we'd
> > > > do that by having the driver register some iio_triggers and depending
> > > > on which one is selected do the equivalent of what you have here.
> > > >  
> > > Agreed for Asynchronous and Synchronous triggers. WRT Software trigger
> > > should this be registered as a  iio_triggers too or read_raw()
> > > callback (with IIO_CHAN_INFO_RAW case)  should be treated as Software
> > > trigger?
> > >  
> >
> > Normally we'd use an external trigger to provide the software trigger
> > (plus as you say sysfs reads will map to this functionality).
> >
> > Something like the sysfs trigger or the hrtimer one would get used, though
> > also fine to use the dataready trigger from a different device (if you want
> > approximately synced dta.
> >  
> We can live with syfs reads for now for SW triggers. Coming back to HW
> triggers I responded too quickly!. I am now trying to implement a gpio
> based HW trigger i.e. to kick adc conversion start but I couldn't find
> any drivers doing that. I looked at iio-trig-interrupt.c which
> registers irq based triggers, so something similar needs to be
> implemented in the adc driver? If that is the case the gpio has to be
> passed via to DT and use gpio_to_irq to register the handler. Or is it
> that I am missing something here ?

Ok, I'm not really following the usecase for this. Is the thought that you'll
get lower latency / jitter triggering via a gpio rather than using a
bus write to the device (though on an integrated ADC I can't see why that would
be the case)?

If so, then what is actually setting the gpio?  Something is ultimately
acting as the real trigger.  A common model would be an hrtimer trigger
for example.   If you then want to wire the driver up to capture on demand
using the gpio (to reduce latency) that's fine, but the gpio itself is
never a trigger in the sense of an IIO trigger (rather than a trigger
to the ADC itself).  In that case, have the trigger handler set the
the gpio and wait for data capture to finish.  Quite a few drivers
do this as some devices can only start sampling on an external pin being
set.  E.g. adc/ad7606.c 

The iio-trig-interrupt is about using an external interrupt to trigger
a capture initialized by a register write or similar, it's not a direct
hardware capture signal.

Jonathan

> 
> Cheers,
> Prabhakar
> 
> > > > > +    default: 0
> > > > > +
> > > > > +  gpios:
> > > > > +    description:
> > > > > +      ADC_TRG trigger input pin
> > > > > +    maxItems: 1  
> > > > Why is this mode useful?  I'm assuming the gpio write would take a register
> > > > write and the software trigger mode also requires a register write.
> > > >  
> > > Yes gpio write would take a register write.
> > >  
> > > > Normally the reason for a pin like this is to support synchronising with
> > > > external hardware.   If that's the case, we should call that out here.
> > > > often the pin isn't even connected to a gpio in our control.
> > > > (i.e. it's a trigger signal from some other device.)
> > > >  
> > > So just setting the GPIO pin as input should do the trick.  
> >
> > Probably the best plan if you actually care about people writing some
> > trigger up to it that is otherwise invisible to the system.
> >  
> > >  
> > > > > +
> > > > > +  renesas-rzg2l,adc-channels:
> > > > > +    $ref: /schemas/types.yaml#/definitions/uint8-array
> > > > > +    description: Input channels available on platform
> > > > > +    uniqueItems: true
> > > > > +    minItems: 1
> > > > > +    maxItems: 8
> > > > > +    items:
> > > > > +      enum: [0, 1, 2, 3, 4, 5, 6, 7]  
> > > >
> > > > Is this a function of different devices (should have different compatibles)
> > > > or of what is wired up.  If it's what is wired up, then how do you know which  
> > > Its channels which are wired, for example if channels 0-5 are wired up
> > > the board dts would include the property "renesas-rzg2l,adc-channels =
> > > /bits/ 8 <0 1 2 3 4 5>;"
> > >  
> > > > subset of channels are connected?  We have the generic adc channel binding
> > > > in iio/adc/adc.yaml for the case where we only want to expose those channels
> > > > that are wired up.  It uses a node per channel.
> > > >  
> > > Agreed will do that and drop the custom "renesas-rzg2l,adc-channels"  
> >
> > Great,
> >
> > Jonathan
> >  
> > >
> > > Cheers,
> > > Prabhakar  
> > > > > +
> > > > > +  "#io-channel-cells":
> > > > > +    const: 1
> > > > > +
> > > > > +required:
> > > > > +  - compatible
> > > > > +  - reg
> > > > > +  - interrupts
> > > > > +  - clocks
> > > > > +  - clock-names
> > > > > +  - power-domains
> > > > > +  - resets
> > > > > +  - reset-names
> > > > > +  - renesas-rzg2l,adc-channels
> > > > > +  - "#io-channel-cells"
> > > > > +
> > > > > +allOf:
> > > > > +  - if:
> > > > > +      properties:
> > > > > +        renesas-rzg2l,adc-trigger-mode:
> > > > > +          const: 1
> > > > > +    then:
> > > > > +      required:
> > > > > +        - gpios
> > > > > +
> > > > > +additionalProperties: false
> > > > > +
> > > > > +examples:
> > > > > +  - |
> > > > > +    #include <dt-bindings/clock/r9a07g044-cpg.h>
> > > > > +    #include <dt-bindings/interrupt-controller/arm-gic.h>
> > > > > +
> > > > > +    adc: adc@10059000 {
> > > > > +      compatible = "renesas,r9a07g044-adc", "renesas,rzg2l-adc";
> > > > > +      reg = <0x10059000 0x400>;
> > > > > +      interrupts = <GIC_SPI 347 IRQ_TYPE_EDGE_RISING>;
> > > > > +      clocks = <&cpg CPG_MOD R9A07G044_ADC_ADCLK>,
> > > > > +               <&cpg CPG_MOD R9A07G044_ADC_PCLK>;
> > > > > +      clock-names = "adclk", "pclk";
> > > > > +      power-domains = <&cpg>;
> > > > > +      resets = <&cpg R9A07G044_ADC_PRESETN>,
> > > > > +               <&cpg R9A07G044_ADC_ADRST_N>;
> > > > > +      reset-names = "presetn", "adrst-n";
> > > > > +      #io-channel-cells = <1>;
> > > > > +      renesas-rzg2l,adc-trigger-mode = /bits/ 8 <0>;
> > > > > +      renesas-rzg2l,adc-channels = /bits/ 8 <0 1 2 3 4 5 6>;
> > > > > +    };  
> > > >  
> >