Re: [PATCH v1 1/2] dt-bindings: trivial-devices: add spi-miso-mosi-loopback

[Francesco Dolcini <francesco@dolcini.it>]

Hello Krzysztof,
thanks for taking the time to answer this

On Mon, Mar 16, 2026 at 09:36:42AM +0100, Krzysztof Kozlowski wrote:
> On 16/03/2026 09:35, Krzysztof Kozlowski wrote:
> > On 16/03/2026 08:35, Francesco Dolcini wrote:
> >> From: Francesco Dolcini <francesco.dolcini@toradex.com>
> >>
> >> Add a compatible to describe a single wire loopback between SPI MISO and
> >> MOSI signals.
> >>
> >> Link: https://lore.kernel.org/all/20260310133254.GA51497@francesco-nb/
> >> Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> >> ---
> >>  Documentation/devicetree/bindings/trivial-devices.yaml | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/trivial-devices.yaml b/Documentation/devicetree/bindings/trivial-devices.yaml
> >> index a482aeadcd44..2cb973c157f6 100644
> >> --- a/Documentation/devicetree/bindings/trivial-devices.yaml
> >> +++ b/Documentation/devicetree/bindings/trivial-devices.yaml
> >> @@ -432,6 +432,8 @@ properties:
> >>            - socionext,uniphier-smpctrl
> >>              # SparkFun Qwiic Joystick (COM-15168) with i2c interface
> >>            - sparkfun,qwiic-joystick
> >> +            # Single wire loopback between SPI MISO and MOSI signals
> >> +          - spi-miso-mosi-loopback
> > 
> > If you decided to go against my approach, then at least document it in
> > proper place - incomplete-devices - so this won't be ever used in DTS.
> >
> 
> ... and then you will notice existing linux,spi-loopback-test, so
> explain the differences and why spi-loopback-test cannot be used for
> your loopback test.

Yes, this spi-loopback-test will work.

I was not aware of it (no-one mentioned it in the email thread I opened)
and I misread your answer as an alternative suggestion, and not as a nack.

There is still an open question, I can any driver probe/bind to the
actual SPI device? My plan, once this discussion is settled, is to send
patches to add dtso file enabling this test, however, according to
trivial-devices.yaml, I cannot submit such a DT file using
linux,spi-loopback-test as a compatible.

On the actual HW I have a pins header and a wire between MISO/MOSI.

I am clearly missing something obvious, any advise is appreciated.

Thanks,
Francesco