linux-kernel - Re: [PATCH v2 3/3] dt-bindings: adis16460: Add 'spi-cs-inactive-delay-ns' property

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Date:   Tue, 24 Oct 2023 08:53:14 +0200
From:   Nuno Sá <noname.nuno@...il.com>
To:     Conor Dooley <conor@...nel.org>
Cc:     Ramona Gradinariu <ramona.gradinariu@...log.com>, jic23@...nel.org,
        nuno.sa@...log.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 3/3] dt-bindings: adis16460: Add
 'spi-cs-inactive-delay-ns' property

On Mon, 2023-10-23 at 17:06 +0100, Conor Dooley wrote:
> On Mon, Oct 23, 2023 at 04:27:48PM +0200, Nuno Sá wrote:
> > On Mon, 2023-10-23 at 17:05 +0300, Ramona Gradinariu wrote:
> > > The adis16460 device requires a stall time between SPI
> > > transactions (during which the chip select is inactive),
> > > with a minimum value equal to 16 microseconds.
> > > This commit adds 'spi-cs-inactive-delay-ns' property, which should
> > > indicate the stall time between consecutive SPI transactions.
> > > 
> > > Signed-off-by: Ramona Gradinariu <ramona.gradinariu@...log.com>
> > > ---
> > > changes in v2:
> > >  - added default value
> > >  - updated description
> > >  - updated commit message
> > >  .../devicetree/bindings/iio/imu/adi,adis16460.yaml          | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/iio/imu/adi,adis16460.yaml
> > > b/Documentation/devicetree/bindings/iio/imu/adi,adis16460.yaml
> > > index 4e43c80e5119..f10469b86ee0 100644
> > > --- a/Documentation/devicetree/bindings/iio/imu/adi,adis16460.yaml
> > > +++ b/Documentation/devicetree/bindings/iio/imu/adi,adis16460.yaml
> > > @@ -25,6 +25,12 @@ properties:
> > > 
> > >    spi-cpol: true
> > > 
> > > +  spi-cs-inactive-delay-ns:
> > > +    minimum: 16000
> > > +    default: 16000
> > > +    description:
> > > +      Indicates the stall time between consecutive SPI transactions.
> > > +
> > 
> > You should drop the description... 
> > 
> > Also, give more time before posting a v2 so others get a chance to review
> > your
> > patches. It's also better for you since you can gather more change requests.
> 
> Further, I don't see an answer to Krzysztof's question of why the stall
> time would not just be set to 16,000 ns in the driver, based on the
> compatible.

Hi Conor,

Regarding that, I'm the one to blame since I was the one asking for the property
during internal review... The reason is that "spi-cs-inactive-delay-ns" is
already part of spi-peripheral-props.yaml which we already reference. So my
question would be why not using it?

These devices are a bit sensitive regarding these timings. Not in devices
supported by this driver but I already experienced having to set timings bigger
than defined in the datasheet for spi to be reliable. this was true on a RPI but
might not be in another platform.

Hence having the flexibility to change the time in an already supported property
does sound good to me. If not set, we still use the default value based on the
compatible. Now, if you tell me "let's just add this if we really get the need
for it", I get it but I also don't understand why not add it now...

Thanks!
- Nuno Sá