Re: [PATCH v2 2/4] iio: backend: add devm_iio_backend_get_by_index()

[Nuno Sá]

On Fri, 2026-02-06 at 18:07 +0200, Antoniu Miclaus wrote:
> Add a new function to get an IIO backend by its index in the
> io-backends device tree property. This is useful for multi-channel
> devices that have multiple backends, where looking up by index is
> more straightforward than using named backends.
> 
> The new function directly uses the index to find the backend reference
> in the io-backends property, avoiding the need for io-backend-names.
> 
> Signed-off-by: Antoniu Miclaus <antoniu.miclaus@xxxxxxxxxx>
> ---
>  drivers/iio/industrialio-backend.c | 51 ++++++++++++++++++++++++++++++
>  include/linux/iio/backend.h        |  2 ++
>  2 files changed, 53 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-
> backend.c
> index 447b694d6d5f..3b692d48481e 100644
> --- a/drivers/iio/industrialio-backend.c
> +++ b/drivers/iio/industrialio-backend.c
> @@ -1008,6 +1008,57 @@ struct iio_backend *devm_iio_backend_get(struct device *dev,
> const char *name)
>  }
>  EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get, "IIO_BACKEND");
>  
> +static struct iio_backend *
> +__devm_iio_backend_fwnode_get_by_index(struct device *dev,
> +				       struct fwnode_handle *fwnode,
> +				       unsigned int index)
> +{
> +	struct fwnode_handle *fwnode_back;
> +	struct iio_backend *back;
> +	int ret;
> +
> +	fwnode_back = fwnode_find_reference(fwnode, "io-backends", index);
> +	if (IS_ERR(fwnode_back))
> +		return dev_err_cast_probe(dev, fwnode_back,
> +					  "Cannot get Firmware reference\n");
> +
> +	guard(mutex)(&iio_back_lock);
> +	list_for_each_entry(back, &iio_back_list, entry) {
> +		if (!device_match_fwnode(back->dev, fwnode_back))
> +			continue;
> +
> +		fwnode_handle_put(fwnode_back);
> +		ret = __devm_iio_backend_get(dev, back);
> +		if (ret)
> +			return ERR_PTR(ret);
> +
> +		back->idx = index;
> +
> +		return back;
> +	}
> +
> +	fwnode_handle_put(fwnode_back);
> +	return ERR_PTR(-EPROBE_DEFER);
> +}

I believe we don't necessarily need this. Why can't we use io-backend-names? I get
that in here we just want something matching the number of channels we have so giving
names is probably does not add much added value. But still, I would prefer t have
more simplicity in the API and it should be fairly easy for the frontend to use the
names argument.

_ Nuno Sá