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.

Extract __devm_iio_backend_fwnode_get_by_index() from the existing
__devm_iio_backend_fwnode_get(), taking the index directly as a
parameter. The new public API devm_iio_backend_get_by_index() uses
the index to find the backend reference in the io-backends property,
avoiding the need for io-backend-names.

Reviewed-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
---
Changes in v8:
  - No changes

 drivers/iio/industrialio-backend.c | 53 +++++++++++++++++++++---------
 include/linux/iio/backend.h        |  1 +
 2 files changed, 39 insertions(+), 15 deletions(-)

diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
index 58f7e1426095..d6e922c65347 100644
--- a/drivers/iio/industrialio-backend.c
+++ b/drivers/iio/industrialio-backend.c
@@ -949,23 +949,13 @@ 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 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;
-	}
-
 	struct fwnode_handle *fwnode_back __free(fwnode_handle) =
 		fwnode_find_reference(fwnode, "io-backends", index);
 	if (IS_ERR(fwnode_back))
@@ -981,8 +971,7 @@ static struct iio_backend *__devm_iio_backend_fwnode_get(struct device *dev, con
 		if (ret)
 			return ERR_PTR(ret);
 
-		if (name)
-			back->idx = index;
+		back->idx = index;
 
 		return back;
 	}
@@ -990,6 +979,24 @@ static struct iio_backend *__devm_iio_backend_fwnode_get(struct device *dev, con
 	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;
+	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;
+	}
+
+	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
@@ -1006,6 +1013,22 @@ 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
+ *
+ * Gets 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..ce2263d4c2de 100644
--- a/include/linux/iio/backend.h
+++ b/include/linux/iio/backend.h
@@ -237,6 +237,7 @@ 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);
-- 
2.43.0