Re: [PATCH v4 3/5] iio: backend: add devm_iio_backend_get_by_index()

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 23 Feb 2026 18:21:02 +0200
Antoniu Miclaus <antoniu.miclaus@analog.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.
> 
> Reviewed-by: Nuno Sá <nuno.sa@analog.com>
> Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Hi Antoniu,

I'm seeing the use of __free as an unrelated change that I'd prefer
to see as a precusor cleanup patch.

Thanks,

Jonathan

> ---
> Changes in v4:
>   - Add Reviewed-by from Nuno Sá
> 
>  drivers/iio/industrialio-backend.c | 61 ++++++++++++++++++++----------
>  include/linux/iio/backend.h        |  2 +
>  2 files changed, 44 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
> index 447b694d6d5f..d90a3a0b17c6 100644
> --- a/drivers/iio/industrialio-backend.c
> +++ b/drivers/iio/industrialio-backend.c
> @@ -949,25 +949,16 @@ int iio_backend_data_transfer_addr(struct iio_backend *back, u32 address)
>  }
>  EXPORT_SYMBOL_NS_GPL(iio_backend_data_transfer_addr, "IIO_BACKEND");
>  
> -static struct iio_backend *__devm_iio_backend_fwnode_get(struct device *dev, const char *name,
> -							 struct fwnode_handle *fwnode)
> +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 fwnode_handle *fwnode_back __free(fwnode_handle) =
> +		fwnode_find_reference(fwnode, "io-backends", index);

This use of __free is a refactor, that you are doing whilst you happen to be here.
Really should be in a separate precursor patch so that we can more
easily see what the real code movement going on here is about.

>  	struct iio_backend *back;
> -	unsigned int index;
>  	int ret;
>  
> -	if (name) {
> -		ret = device_property_match_string(dev, "io-backend-names",
> -						   name);
> -		if (ret < 0)
> -			return ERR_PTR(ret);
> -		index = ret;
> -	} else {
> -		index = 0;
> -	}
> -
> -	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");
> @@ -977,21 +968,35 @@ static struct iio_backend *__devm_iio_backend_fwnode_get(struct device *dev, con
>  		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);
>  
> -		if (name)
> -			back->idx = index;
> +		back->idx = index;
>  
>  		return back;
>  	}
>  
> -	fwnode_handle_put(fwnode_back);
>  	return ERR_PTR(-EPROBE_DEFER);
>  }
>  
> +static struct iio_backend *__devm_iio_backend_fwnode_get(struct device *dev, const char *name,
> +							 struct fwnode_handle *fwnode)
> +{
> +	unsigned int index = 0;
> +	int ret;
> +
> +	if (name) {
> +		ret = device_property_match_string(dev, "io-backend-names",
> +						   name);
> +		if (ret < 0)
> +			return ERR_PTR(ret);
> +		index = ret;
> +	}
> +
> +	return __devm_iio_backend_fwnode_get_by_index(dev, fwnode, index);
> +}
> +
>  /**
>   * devm_iio_backend_get - Device managed backend device get
>   * @dev: Consumer device for the backend
> @@ -1008,6 +1013,24 @@ struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
>  }
>  EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get, "IIO_BACKEND");
>  
> +/**
> + * 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.
Gets 

It could either be 
Get us (in which case our Get's is valid) or Gets as it the function is
responsible for getting.  I think Gets is more natural here.

> + *
> + * 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);