platform/chrome: cros_ec_chardev: Add event relayer

Introduce an event relayer mechanism.  Instead of each open file
registering directly with `ec_dev->event_notifier`, the platform device
registers a single relayer notifier.  Individual files then register
with a local subscribers list in `chardev_pdata`.

This allows the driver to safely disconnect from the event chain
`ec_dev->event_notifier` during cros_ec_chardev_remove(), preventing
events from being delivered to open files after the device is removed,
while still allowing those files to be closed safely later.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20260525052654.4076429-4-tzungbi@kernel.org
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

diff --git a/drivers/platform/chrome/cros_ec_chardev.c b/drivers/platform/chrome/cros_ec_chardev.c
index 352d61a2f3c6e2b4d1e09b44f14fef02c100dae8..7e046fc56998db3203e449b4e755d1e0cbe4b849 100644 (file)
--- a/drivers/platform/chrome/cros_ec_chardev.c
+++ b/drivers/platform/chrome/cros_ec_chardev.c
@@ -40,6 +40,8 @@ struct chardev_pdata {
        struct kref kref;
        struct cros_ec_device *ec_dev;
        u16 cmd_offset;
+       struct blocking_notifier_head subscribers;
+       struct notifier_block relay;
 };
 
 static void chardev_pdata_release(struct kref *kref)
@@ -49,6 +51,17 @@ static void chardev_pdata_release(struct kref *kref)
        kfree(pdata);
 }
 
+static int cros_ec_chardev_relay_event(struct notifier_block *nb,
+                                      unsigned long queued_during_suspend,
+                                      void *_notify)
+{
+       struct chardev_pdata *pdata = container_of(nb, typeof(*pdata), relay);
+
+       blocking_notifier_call_chain(&pdata->subscribers, queued_during_suspend,
+                                    _notify);
+       return NOTIFY_OK;
+}
+
 struct chardev_priv {
        struct notifier_block notifier;
        wait_queue_head_t wait_event;
@@ -190,7 +203,7 @@ static int cros_ec_chardev_open(struct inode *inode, struct file *filp)
        nonseekable_open(inode, filp);
 
        priv->notifier.notifier_call = cros_ec_chardev_mkbp_event;
-       ret = blocking_notifier_chain_register(&pdata->ec_dev->event_notifier,
+       ret = blocking_notifier_chain_register(&pdata->subscribers,
                                               &priv->notifier);
        if (ret) {
                dev_err(pdata->ec_dev->dev,
@@ -271,7 +284,7 @@ static int cros_ec_chardev_release(struct inode *inode, struct file *filp)
        struct chardev_priv *priv = filp->private_data;
        struct ec_event *event, *e;
 
-       blocking_notifier_chain_unregister(&priv->pdata->ec_dev->event_notifier,
+       blocking_notifier_chain_unregister(&priv->pdata->subscribers,
                                           &priv->notifier);
        kref_put(&priv->pdata->kref, chardev_pdata_release);
 
@@ -403,6 +416,14 @@ static int cros_ec_chardev_probe(struct platform_device *pdev)
        kref_init(&pdata->kref);
        pdata->ec_dev = ec->ec_dev;
        pdata->cmd_offset = ec->cmd_offset;
+       BLOCKING_INIT_NOTIFIER_HEAD(&pdata->subscribers);
+       pdata->relay.notifier_call = cros_ec_chardev_relay_event;
+       ret = blocking_notifier_chain_register(&pdata->ec_dev->event_notifier,
+                                              &pdata->relay);
+       if (ret) {
+               dev_err(&pdev->dev, "failed to register event notifier\n");
+               goto err_put_pdata;
+       }
 
        pdata->misc.minor = MISC_DYNAMIC_MINOR;
        pdata->misc.fops = &chardev_fops;
@@ -412,10 +433,13 @@ static int cros_ec_chardev_probe(struct platform_device *pdev)
        ret = misc_register(&pdata->misc);
        if (ret) {
                dev_err(&pdev->dev, "failed to register misc device\n");
-               goto err_put_pdata;
+               goto err_unregister_notifier;
        }
 
        return 0;
+err_unregister_notifier:
+       blocking_notifier_chain_unregister(&pdata->ec_dev->event_notifier,
+                                          &pdata->relay);
 err_put_pdata:
        kref_put(&pdata->kref, chardev_pdata_release);
        return ret;
@@ -425,6 +449,8 @@ static void cros_ec_chardev_remove(struct platform_device *pdev)
 {
        struct chardev_pdata *pdata = platform_get_drvdata(pdev);
 
+       blocking_notifier_chain_unregister(&pdata->ec_dev->event_notifier,
+                                          &pdata->relay);
        misc_deregister(&pdata->misc);
        kref_put(&pdata->kref, chardev_pdata_release);
 }