[RFC v2 01/11] iio: introduce iio backend device

[Olivier Moysan <olivier.moysan@foss.st.com>]

Add a new device type in IIO framework.
This backend device does not compute channel attributes and does not expose
them through sysfs, as done typically in iio-rescale frontend device.
Instead, it allows to report information applying to channel
attributes through callbacks. These backend devices can be cascaded
to represent chained components.
An IIO device configured as a consumer of a backend device can compute
the channel attributes of the whole chain.

Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
---
 drivers/iio/Makefile               |   1 +
 drivers/iio/industrialio-backend.c | 107 +++++++++++++++++++++++++++++
 include/linux/iio/backend.h        |  56 +++++++++++++++
 3 files changed, 164 insertions(+)
 create mode 100644 drivers/iio/industrialio-backend.c
 create mode 100644 include/linux/iio/backend.h

diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
index 9622347a1c1b..9b59c6ab1738 100644
--- a/drivers/iio/Makefile
+++ b/drivers/iio/Makefile
@@ -5,6 +5,7 @@
 
 obj-$(CONFIG_IIO) += industrialio.o
 industrialio-y := industrialio-core.o industrialio-event.o inkern.o
+industrialio-$(CONFIG_IIO_BACKEND) += industrialio-backend.o
 industrialio-$(CONFIG_IIO_BUFFER) += industrialio-buffer.o
 industrialio-$(CONFIG_IIO_TRIGGER) += industrialio-trigger.o
 
diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
new file mode 100644
index 000000000000..7d0625889873
--- /dev/null
+++ b/drivers/iio/industrialio-backend.c
@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: GPL-2.0
+/* The industrial I/O core, backend handling functions
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/property.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/backend.h>
+
+static DEFINE_IDA(iio_backend_ida);
+
+#define to_iio_backend(_device) container_of((_device), struct iio_backend, dev)
+
+static void iio_backend_release(struct device *device)
+{
+	struct iio_backend *backend = to_iio_backend(device);
+
+	kfree(backend->name);
+	kfree(backend);
+}
+
+static const struct device_type iio_backend_type = {
+	.release = iio_backend_release,
+	.name = "iio_backend_device",
+};
+
+struct iio_backend *iio_backend_alloc(struct device *parent)
+{
+	struct iio_backend *backend;
+
+	backend = devm_kzalloc(parent, sizeof(*backend), GFP_KERNEL);
+
+	backend->dev.parent = parent;
+	backend->dev.type = &iio_backend_type;
+	backend->dev.bus = &iio_bus_type;
+	device_initialize(&backend->dev);
+
+	return backend;
+};
+EXPORT_SYMBOL(iio_backend_alloc);
+
+void iio_backend_free(struct device *dev)
+{
+	if (dev)
+		put_device(dev);
+}
+EXPORT_SYMBOL(iio_backend_free);
+
+int iio_backend_register(struct iio_backend *backend)
+{
+	struct fwnode_handle *fwnode;
+	int id;
+
+	id = ida_alloc(&iio_backend_ida, GFP_KERNEL);
+	if (id < 0)
+		return id;
+	backend->id = id;
+
+	dev_set_name(&backend->dev, "backend%d", backend->id);
+
+	if (dev_fwnode(&backend->dev))
+		fwnode = dev_fwnode(&backend->dev);
+	else
+		fwnode = dev_fwnode(backend->dev.parent);
+	device_set_node(&backend->dev, fwnode);
+
+	return device_add(&backend->dev);
+};
+EXPORT_SYMBOL(iio_backend_register);
+
+void iio_backend_unregister(struct iio_backend *backend)
+{
+	device_del(&backend->dev);
+};
+EXPORT_SYMBOL(iio_backend_unregister);
+
+struct iio_backend *fwnode_iio_backend_get(struct fwnode_handle *fwnode, int index)
+{
+	struct iio_backend *backend;
+	struct fwnode_reference_args iiospec;
+	struct device *bdev;
+	int ret;
+
+	if (index < 0)
+		return ERR_PTR(-EINVAL);
+
+	ret = fwnode_property_get_reference_args(fwnode, "io-backends",
+						 "#io-backend-cells", 0,
+						 index, &iiospec);
+	if (ret)
+		return ERR_PTR(ret);
+
+	bdev = bus_find_device_by_fwnode(&iio_bus_type, iiospec.fwnode);
+	if (!bdev) {
+		fwnode_handle_put(iiospec.fwnode);
+		return ERR_PTR(-EPROBE_DEFER);
+	}
+
+	backend = to_iio_backend(bdev);
+
+	fwnode_handle_put(iiospec.fwnode);
+
+	return backend;
+};
+EXPORT_SYMBOL(fwnode_iio_backend_get);
diff --git a/include/linux/iio/backend.h b/include/linux/iio/backend.h
new file mode 100644
index 000000000000..d90d345a4625
--- /dev/null
+++ b/include/linux/iio/backend.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * The industrial I/O core, backend handling functions
+ *
+ * Author: Olivier Moysan <olivier.moysan@foss.st.com>.
+ */
+
+#ifndef _IIO_BACKEND_H_
+#define _IIO_BACKEND_H_
+#include <linux/iio/iio.h>
+
+struct iio_backend_ops;
+struct iio_backend;
+
+/**
+ * struct iio_backend_ops - operations structure for an iio_backend
+ * @enable:	switch on backend
+ * @disable:	switch off backend
+ * @read_raw:	read data from backend
+ **/
+struct iio_backend_ops {
+	int (*enable)(struct iio_backend *backend);
+	int (*disable)(struct iio_backend *backend);
+	int (*read_raw)(struct iio_backend *backend, int *val, int *val2, long mask);
+};
+
+/**
+ * truct iio_backend - industrial I/O backend device
+ * @ops:	operations structure
+ * @module:	owner of this driver module
+ * @id:		unique id number
+ * @name:	unique name
+ * @dev:	associated device
+ * @priv:	private data pointer
+ **/
+struct iio_backend {
+	const struct iio_backend_ops	*ops;
+	struct module			*owner;
+	int				id;
+	const char			*name;
+	struct device			dev;
+	struct list_head		list;
+	void				*priv;
+};
+
+struct iio_backend *iio_backend_alloc(struct device *parent);
+
+void iio_backend_free(struct device *dev);
+
+int iio_backend_register(struct iio_backend *backend);
+
+void iio_backend_unregister(struct iio_backend *backend);
+
+struct iio_backend *fwnode_iio_backend_get(struct fwnode_handle *fwnode, int index);
+
+#endif /* _IIO_BACKEND_H_ */
-- 
2.25.1