Re: [RFC 1/5] misc: introduce notify-device driver

A notify-device is a synchronization facility that allows to query
"readiness" across drivers, without creating a direct dependency between
the driver modules. The notify-device can also be used to trigger deferred
probes.

Signed-off-by: Matthias Schiffer <redacted>
---
 drivers/misc/Kconfig          |   4 ++
 drivers/misc/Makefile         |   1 +
 drivers/misc/notify-device.c  | 109 ++++++++++++++++++++++++++++++++++
 include/linux/notify-device.h |  33 ++++++++++
 4 files changed, 147 insertions(+)
 create mode 100644 drivers/misc/notify-device.c
 create mode 100644 include/linux/notify-device.h

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 358ad56f6524..63559e9f854c 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig

@@ -496,6 +496,10 @@ config VCPU_STALL_DETECTOR
 
 	  If you do not intend to run this kernel as a guest, say N.
 
+config NOTIFY_DEVICE
+	tristate "Notify device"
+	depends on OF
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"

diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index ac9b3e757ba1..1e8012112b43 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile

@@ -62,3 +62,4 @@ obj-$(CONFIG_HI6421V600_IRQ)	+= hi6421v600-irq.o
 obj-$(CONFIG_OPEN_DICE)		+= open-dice.o
 obj-$(CONFIG_GP_PCI1XXXX)	+= mchp_pci1xxxx/
 obj-$(CONFIG_VCPU_STALL_DETECTOR)	+= vcpu_stall_detector.o
+obj-$(CONFIG_NOTIFY_DEVICE)	+= notify-device.o

diff --git a/drivers/misc/notify-device.c b/drivers/misc/notify-device.c
new file mode 100644
index 000000000000..42e0980394ea
--- /dev/null
+++ b/drivers/misc/notify-device.c

@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/device/class.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/notify-device.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+static void notify_device_release(struct device *dev)
+{
+	of_node_put(dev->of_node);
+	kfree(dev);
+}
+
+static struct class notify_device_class = {
+	.name = "notify-device",
+	.owner = THIS_MODULE,
+	.dev_release = notify_device_release,
+};
+
+static struct platform_driver notify_device_driver = {