Re: [PATCH 02/10] iio: backend: add devm_iio_backend_get_optional()

[Nuno Sá]

On Thu, Oct 15, 2026 at 09:41:40PM +0300, Andy Shevchenko wrote:
> On Thu, Oct 15, 2026 at 01:49:42PM -0300, Rodrigo Alencar via B4 Relay wrote:
> 
> > Frontend devices might not need a backend driver to rely on. An IIO device
> > that supports backends can behave differently when they are not available
> > and that should be acceptable. Such parts may provide basic functionality
> > solely using the control interface (SPI for instance), being able to have
> > extended features when a backend is present.
> > 
> > Add devm_iio_backend_get_optional(), which returns NULL when the backend
> > is not described in firmware, i.e., when the io-backends property is not
> > present or, for a named lookup, when the name is not listed in the
> > io-backend-names property. Other errors, such as probe deferral, are
> > still returned.
> > 
> > To make that possible, a named lookup that does not match any entry of
> > io-backend-names now fails with -ENOENT, the same error returned when the
> > io-backends reference is missing. Also, the missing reference is no longer
> > logged as an error, leaving that to the caller.
> 
> ...
> 
> >  	struct fwnode_handle *fwnode_back __free(fwnode_handle) =
> >  		fwnode_find_reference(fwnode, "io-backends", index);
> > -	if (IS_ERR(fwnode_back))
> > +	if (IS_ERR(fwnode_back)) {
> > +		/* not described in firmware, let the caller decide what to do */
> > +		if (PTR_ERR(fwnode_back) == -ENOENT)
> > +			return ERR_CAST(fwnode_back);
> > +
> >  		return dev_err_cast_probe(dev, fwnode_back,
> >  					  "Cannot get Firmware reference\n");
> > +	}
> 
> Simpler to do is just to add
> 
> 	/* not described in firmware, let the caller decide what to do */
> 	if (PTR_ERR(fwnode_back) == -ENOENT)
> 		return ERR_CAST(fwnode_back);
> 
> just before IS_ERR() check.
> 
> ...
> 
> >  		ret = device_property_match_string(dev, "io-backend-names", name);
> > +		if (ret == -EINVAL || ret == -ENODATA)
> > +			return ERR_PTR(-ENOENT);
> 
> No. Please, use device_property_present() instead.

Oh right! Totally forgot about that internally :). And it fits into my
internal point where I don't agree much in treating -ENODATA the same
way as property does not exist.

- Nuno Sá

> 
> >  		if (ret < 0)
> >  			return ERR_PTR(ret);
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>