Re: SPI loopback tests

[Conor Dooley <conor@kernel.org>]

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On Tue, Mar 10, 2026 at 03:55:51PM +0000, Mark Brown wrote:
> On Tue, Mar 10, 2026 at 02:32:54PM +0100, Francesco Dolcini wrote:
> 
> > So far to test this we had some out-of-tree DT overlay abusing the spidev
> > compatible, however we'd like to move away from this approach and have a
> > solution that is 100% in mainline.
> 
> > Manually unbinding/binding the driver in userspace does not seems as an
> > option, because there is no device node.
> 
> > One option that I could think of would be to add a new compatible that
> > to describe this single wire loopback connection (something like
> > `linux,spi-miso-mosi-loopback`) that would bind to the spidev driver.
> 
> > I am aware that you all DT maintainers shared in a pretty clear way your
> > view on the abuse of the spidev multiple times.
> 
> > What would you be your advice to handle the need of an SPI loopback
> > test? Am I missing something and there is a solution already available?
> 
> I'm not aware of any idiomatic way to deal with this with DT
> unfortunately.  Perhaps the DT people have some ideas here?

I dunno, the suggestion seems fairly reasonable to me. I don't think
it's really abuse of anything, because the compatible would represent a
real hardware configuration. The only think that feels "abusive" is the
fake reg property you'd need.

Not sure that there should be a "linux," vendor prefix though, there's
nothing linux-specific about doing loopback. Probably should be
vendor-less?



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