[PATCH v2] fpga: mgr: add notifier for manager register/unregister events

[Anatolij Gustschin <agust@denx.de>]

Add API functions for registering and removing a notifier for FPGA
manager register/unregister events. Notify when a new FPGA manager
has been registered or when an existing manager is being removed.
This will help configuration interface drivers to get the notion
of low-level FPGA managers appearing or disappearing, when using
hotpluggable FPGA configuration devices (e.g. via USB-FPP or
USB-SPI adapters).

Signed-off-by: Anatolij Gustschin <agust@denx.de>
---
Changes in v2:
 - rebased on v4.20-rc1, reworked documentation
 - also notify about all fpga managers that were registered before
   adding the manager register/unregister notifier

 Documentation/driver-api/fpga/fpga-mgr.rst | 15 ++++++++
 drivers/fpga/fpga-mgr.c                    | 45 ++++++++++++++++++++++
 include/linux/fpga/fpga-mgr.h              | 12 ++++++
 3 files changed, 72 insertions(+)

diff --git a/Documentation/driver-api/fpga/fpga-mgr.rst b/Documentation/driver-api/fpga/fpga-mgr.rst
index 576f1945eacd..fd736a22f5fc 100644
--- a/Documentation/driver-api/fpga/fpga-mgr.rst
+++ b/Documentation/driver-api/fpga/fpga-mgr.rst
@@ -125,3 +125,18 @@ API for implementing a new FPGA Manager driver
 
 .. kernel-doc:: drivers/fpga/fpga-mgr.c
    :functions: fpga_mgr_unregister
+
+Notification about added or removed FPGA managers
+-------------------------------------------------
+
+To register or unregister the notifier callback for signalling
+about the low level FPGA managers being added or removed, use
+
+* :c:func:`fpga_mgr_register_mgr_notifier` —  Add notifier for manager add/remove event
+* :c:func:`fpga_mgr_unregister_mgr_notifier` —  Remove notifier for manager events
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_register_mgr_notifier
+
+.. kernel-doc:: drivers/fpga/fpga-mgr.c
+   :functions: fpga_mgr_unregister_mgr_notifier
diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
index c3866816456a..307717ad9c6d 100644
--- a/drivers/fpga/fpga-mgr.c
+++ b/drivers/fpga/fpga-mgr.c
@@ -21,6 +21,46 @@
 static DEFINE_IDA(fpga_mgr_ida);
 static struct class *fpga_mgr_class;
 
+static BLOCKING_NOTIFIER_HEAD(fpga_mgr_notifier_list);
+
+static int fpga_mgr_notify_registered(struct device *dev, void *data)
+{
+	struct fpga_manager *mgr = to_fpga_manager(dev);
+
+	blocking_notifier_call_chain(&fpga_mgr_notifier_list,
+				     FPGA_MGR_ADD, mgr);
+	return 0;
+}
+
+/**
+ * fpga_mgr_register_mgr_notifier() - register fpga manager notifier callback
+ * @nb: pointer to the notifier block for the callback events.
+ *
+ * Add a notifier callback for FPGA manager changes. These changes are
+ * either FPGA manager being added or removed.
+ */
+void fpga_mgr_register_mgr_notifier(struct notifier_block *nb)
+{
+	blocking_notifier_chain_register(&fpga_mgr_notifier_list, nb);
+
+	class_for_each_device(fpga_mgr_class, NULL, NULL,
+			      fpga_mgr_notify_registered);
+}
+EXPORT_SYMBOL_GPL(fpga_mgr_register_mgr_notifier);
+
+/**
+ * fpga_mgr_unregister_mgr_notifier() - unregister a notifier callback
+ * @nb: pointer to the notifier block for the callback events.
+ *
+ * Remove a notifier callback. fpga_mgr_register_mgr_notifier() must have
+ * been previously called for this function to work properly.
+ */
+void fpga_mgr_unregister_mgr_notifier(struct notifier_block *nb)
+{
+	blocking_notifier_chain_unregister(&fpga_mgr_notifier_list, nb);
+}
+EXPORT_SYMBOL_GPL(fpga_mgr_unregister_mgr_notifier);
+
 /**
  * fpga_image_info_alloc - Allocate a FPGA image info struct
  * @dev: owning device
@@ -700,6 +740,8 @@ int fpga_mgr_register(struct fpga_manager *mgr)
 
 	dev_info(&mgr->dev, "%s registered\n", mgr->name);
 
+	blocking_notifier_call_chain(&fpga_mgr_notifier_list,
+				     FPGA_MGR_ADD, mgr);
 	return 0;
 
 error_device:
@@ -719,6 +761,9 @@ void fpga_mgr_unregister(struct fpga_manager *mgr)
 {
 	dev_info(&mgr->dev, "%s %s\n", __func__, mgr->name);
 
+	blocking_notifier_call_chain(&fpga_mgr_notifier_list,
+				     FPGA_MGR_REMOVE, mgr);
+
 	/*
 	 * If the low level driver provides a method for putting fpga into
 	 * a desired state upon unregister, do it.
diff --git a/include/linux/fpga/fpga-mgr.h b/include/linux/fpga/fpga-mgr.h
index e8ca62b2cb5b..d6eaec80557b 100644
--- a/include/linux/fpga/fpga-mgr.h
+++ b/include/linux/fpga/fpga-mgr.h
@@ -10,6 +10,7 @@
 
 #include <linux/mutex.h>
 #include <linux/platform_device.h>
+#include <linux/notifier.h>
 
 struct fpga_manager;
 struct sg_table;
@@ -202,4 +203,15 @@ struct fpga_manager *devm_fpga_mgr_create(struct device *dev, const char *name,
 					  const struct fpga_manager_ops *mops,
 					  void *priv);
 
+/*
+ * FPGA Manager register notifier events
+ * FPGA_MGR_ADD: a new fpga manager has been registered
+ * FPGA_MGR_REMOVE: a registered fpga manager is being removed
+ */
+#define FPGA_MGR_ADD	1
+#define FPGA_MGR_REMOVE	2
+
+void fpga_mgr_register_mgr_notifier(struct notifier_block *nb);
+void fpga_mgr_unregister_mgr_notifier(struct notifier_block *nb);
+
 #endif /*_LINUX_FPGA_MGR_H */
-- 
2.17.1