linux-kernel - [char-misc-next 3/3] mei: make char device control its own lifetime

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Message-ID: <20250618095433.3943546-4-alexander.usyskin@intel.com>
Date: Wed, 18 Jun 2025 12:54:33 +0300
From: Alexander Usyskin <alexander.usyskin@...el.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Reuven Abliyev <reuven.abliyev@...el.com>,
	Alexander Usyskin <alexander.usyskin@...el.com>,
	linux-kernel@...r.kernel.org
Subject: [char-misc-next 3/3] mei: make char device control its own lifetime

Allocate character device dynamically and allow to
control its own lifetime as it may outlive mei_device
structure while character device closes after parent
device is removed from the system.

Signed-off-by: Alexander Usyskin <alexander.usyskin@...el.com>
---
 drivers/misc/mei/main.c    | 34 +++++++++++++++++++++-------------
 drivers/misc/mei/mei_dev.h |  4 ++--
 2 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/drivers/misc/mei/main.c b/drivers/misc/mei/main.c
index c160703d0782..2162a8de9e6a 100644
--- a/drivers/misc/mei/main.c
+++ b/drivers/misc/mei/main.c
@@ -51,7 +51,7 @@ static int mei_open(struct inode *inode, struct file *file)
 
 	int err;
 
-	dev = mei_device_get(container_of(inode->i_cdev, struct mei_device, cdev));
+	dev = mei_device_get(idr_find(&mei_idr, iminor(inode)));
 	if (!dev)
 		return -ENODEV;
 
@@ -1122,7 +1122,10 @@ void mei_set_devstate(struct mei_device *dev, enum mei_dev_state state)
 
 	dev->dev_state = state;
 
-	clsdev = class_find_device_by_devt(&mei_class, dev->cdev.dev);
+	if (!dev->cdev)
+		return;
+
+	clsdev = class_find_device_by_devt(&mei_class, dev->cdev->dev);
 	if (clsdev) {
 		sysfs_notify(&clsdev->kobj, NULL, "dev_state");
 		put_device(clsdev);
@@ -1227,16 +1230,21 @@ int mei_register(struct mei_device *dev, struct device *parent)
 
 	/* Fill in the data structures */
 	devno = MKDEV(MAJOR(mei_devt), dev->minor);
-	cdev_init(&dev->cdev, &mei_fops);
-	dev->cdev.owner = parent->driver->owner;
-	cdev_set_parent(&dev->cdev, &parent->kobj);
+	dev->cdev = cdev_alloc();
+	if (!dev->cdev) {
+		ret = -ENOMEM;
+		goto err;
+	}
+	dev->cdev->ops = &mei_fops;
+	dev->cdev->owner = parent->driver->owner;
+	cdev_set_parent(dev->cdev, &parent->kobj);
 
 	/* Add the device */
-	ret = cdev_add(&dev->cdev, devno, 1);
+	ret = cdev_add(dev->cdev, devno, 1);
 	if (ret) {
 		dev_err(parent, "unable to add device %d:%d\n",
 			MAJOR(mei_devt), dev->minor);
-		goto err_dev_add;
+		goto err_del_cdev;
 	}
 
 	clsdev = device_create_with_groups(&mei_class, parent, devno,
@@ -1247,16 +1255,16 @@ int mei_register(struct mei_device *dev, struct device *parent)
 		dev_err(parent, "unable to create device %d:%d\n",
 			MAJOR(mei_devt), dev->minor);
 		ret = PTR_ERR(clsdev);
-		goto err_dev_create;
+		goto err_del_cdev;
 	}
 
 	mei_dbgfs_register(dev, dev_name(clsdev));
 
 	return 0;
 
-err_dev_create:
-	cdev_del(&dev->cdev);
-err_dev_add:
+err_del_cdev:
+	cdev_del(dev->cdev);
+err:
 	mei_minor_free(dev);
 	return ret;
 }
@@ -1266,8 +1274,8 @@ void mei_deregister(struct mei_device *dev)
 {
 	int devno;
 
-	devno = dev->cdev.dev;
-	cdev_del(&dev->cdev);
+	devno = dev->cdev->dev;
+	cdev_del(dev->cdev);
 
 	mei_dbgfs_deregister(dev);
 
diff --git a/drivers/misc/mei/mei_dev.h b/drivers/misc/mei/mei_dev.h
index b745cde80662..8f081c6735c4 100644
--- a/drivers/misc/mei/mei_dev.h
+++ b/drivers/misc/mei/mei_dev.h
@@ -471,7 +471,7 @@ struct mei_dev_timeouts {
  * struct mei_device -  MEI private device struct
  *
  * @dev         : device on a bus
- * @cdev        : character device
+ * @cdev        : character device pointer
  * @minor       : minor number allocated for device
  *
  * @refcnt      : struct reference count
@@ -559,7 +559,7 @@ struct mei_dev_timeouts {
  */
 struct mei_device {
 	struct device *dev;
-	struct cdev cdev;
+	struct cdev *cdev;
 	int minor;
 
 	struct kref refcnt;
-- 
2.43.0