linux-kernel - Re: [PATCH v2 2/4] iio: backend: add devm_iio_backend_get_by

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Message-ID: <20260207145731.69c8d842@jic23-huawei>
Date: Sat, 7 Feb 2026 14:57:31 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Antoniu Miclaus <antoniu.miclaus@...log.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich
 <Michael.Hennerich@...log.com>, David Lechner <dlechner@...libre.com>, Nuno
 Sá <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Olivier Moysan
 <olivier.moysan@...s.st.com>, Mark Brown <broonie@...nel.org>,
 <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] iio: backend: add
 devm_iio_backend_get_by_index()

On Fri, 6 Feb 2026 18:07:14 +0200
Antoniu Miclaus <antoniu.miclaus@...log.com> 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@...log.com>
One thing inline.

> ---
>  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);
Applies more generally in this file, but does holding the fwnode over the
__dev_iio_backed_get() below matter?  If not
	struct fwnode_handle *fwnode_back __free(fwnode_handle) =
		fwnode_find_reference(fwnode, "io-backends", index);

and you can drop the various fwnode_handle_put() calls.

> +	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);
> +}
> +
> +/**
> + * devm_iio_backend_get_by_index - Device managed backend device get by index
> + * @dev: Consumer device for the backend
> + * @index: Index of the backend in the io-backends property
> + *
> + * Get's the backend at @index associated with @dev.
> + *
> + * RETURNS:
> + * A backend pointer, negative error pointer otherwise.
> + */
> +struct iio_backend *devm_iio_backend_get_by_index(struct device *dev,
> +						  unsigned int index)
> +{
> +	return __devm_iio_backend_fwnode_get_by_index(dev, dev_fwnode(dev),
> +						      index);
> +}
> +EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get_by_index, "IIO_BACKEND");
> +
>  /**
>   * devm_iio_backend_fwnode_get - Device managed backend firmware node get
>   * @dev: Consumer device for the backend
> diff --git a/include/linux/iio/backend.h b/include/linux/iio/backend.h
> index 7f815f3fed6a..8f18df0ca896 100644
> --- a/include/linux/iio/backend.h
> +++ b/include/linux/iio/backend.h
> @@ -237,6 +237,8 @@ int iio_backend_extend_chan_spec(struct iio_backend *back,
>  				 struct iio_chan_spec *chan);
>  void *iio_backend_get_priv(const struct iio_backend *conv);
>  struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name);
> +struct iio_backend *devm_iio_backend_get_by_index(struct device *dev,
> +						  unsigned int index);
>  struct iio_backend *devm_iio_backend_fwnode_get(struct device *dev,
>  						const char *name,
>  						struct fwnode_handle *fwnode);