Not all backends support the full set of capabilities provided by the
industrialio-backend framework. Capability bits can be used in frontends
and backends for checking for a certain feature set, or if using
related functions can be expected to fail.

Capability bits should be set by a compatible backend and provided when
registering the backend.

Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>
---
 drivers/iio/industrialio-backend.c | 16 ++++++++++++++++
 include/linux/iio/backend.h        | 24 ++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
index 447b694d6d5f..1afd00763da9 100644
--- a/drivers/iio/industrialio-backend.c
+++ b/drivers/iio/industrialio-backend.c
@@ -56,6 +56,7 @@ struct iio_backend {
 	void *priv;
 	const char *name;
 	unsigned int cached_reg_addr;
+	u32 caps;
 	/*
 	 * This index is relative to the frontend. Meaning that for
 	 * frontends with multiple backends, this will be the index of this
@@ -774,6 +775,20 @@ int iio_backend_extend_chan_spec(struct iio_backend *back,
 }
 EXPORT_SYMBOL_NS_GPL(iio_backend_extend_chan_spec, "IIO_BACKEND");
 
+/**
+ * iio_backend_has_caps - Check if backend has specific capabilities
+ * @back: Backend device
+ * @caps: Capabilities to check
+ *
+ * RETURNS:
+ * True if backend has all the requested capabilities, false otherwise.
+ */
+bool iio_backend_has_caps(struct iio_backend *back, u32 caps)
+{
+	return (back->caps & caps) == caps;
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_has_caps, "IIO_BACKEND");
+
 static void iio_backend_release(void *arg)
 {
 	struct iio_backend *back = arg;
@@ -1114,6 +1129,7 @@ int devm_iio_backend_register(struct device *dev,
 
 	back->ops = info->ops;
 	back->name = info->name;
+	back->caps = info->caps;
 	back->owner = dev->driver->owner;
 	back->dev = dev;
 	back->priv = priv;
diff --git a/include/linux/iio/backend.h b/include/linux/iio/backend.h
index 7f815f3fed6a..4d15c2a9802c 100644
--- a/include/linux/iio/backend.h
+++ b/include/linux/iio/backend.h
@@ -84,6 +84,27 @@ enum iio_backend_filter_type {
 	IIO_BACKEND_FILTER_TYPE_MAX
 };
 
+/**
+ * enum iio_backend_capabilities - Backend capabilities
+ * Backend capabilities can be used by frontends to check if a given
+ * functionality is supported by the backend. This is useful for frontend
+ * devices which are expected to work with alternative backend
+ * implementations. Capabilities are loosely coupled with operations,
+ * meaning that a capability requires certain operations to be implemented
+ * by the backend. A capability might be mapped to a single operation or
+ * multiple operations.
+ *
+ * @IIO_BACKEND_CAP_CALIBRATION: Backend supports digital interface
+ * calibration. Calibration procedure is device specific.
+ * @IIO_BACKEND_CAP_BUFFER: Support for IIO buffer interface.
+ * @IIO_BACKEND_CAP_ENABLE: Backend can be explicitly enabled/disabled.
+ */
+enum iio_backend_capabilities {
+	IIO_BACKEND_CAP_CALIBRATION = BIT(0),
+	IIO_BACKEND_CAP_BUFFER = BIT(1),
+	IIO_BACKEND_CAP_ENABLE = BIT(2),
+};
+
 /**
  * struct iio_backend_ops - operations structure for an iio_backend
  * @enable: Enable backend.
@@ -179,10 +200,12 @@ struct iio_backend_ops {
  * struct iio_backend_info - info structure for an iio_backend
  * @name: Backend name.
  * @ops: Backend operations.
+ * @caps: Backend capabilities. (bitmask of enum iio_backend_capabilities).
  */
 struct iio_backend_info {
 	const char *name;
 	const struct iio_backend_ops *ops;
+	u32 caps;
 };
 
 int iio_backend_chan_enable(struct iio_backend *back, unsigned int chan);
@@ -235,6 +258,7 @@ int iio_backend_read_raw(struct iio_backend *back,
 			 long mask);
 int iio_backend_extend_chan_spec(struct iio_backend *back,
 				 struct iio_chan_spec *chan);
+bool iio_backend_has_caps(struct iio_backend *back, u32 caps);
 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_fwnode_get(struct device *dev,

-- 
2.47.3