[PATCH 1/4] driver: core: introduce dev_add_sync_state()

[Brian Masney]

We have cases where a device node represents a provider for multiple
types of resources, like clocks, power-domains, resets, etc. We
currently have dev_set_drv_sync_state() where a framework or driver
can set the sync_state callback for a device node, however it currently
only supports a single sync_state callback.

The pmdomain subsystem currently sets up a sync_state callback in the
core framework, and the clk subsystem will setup it's own separate
sync_state callback in the core framework. These can collide with each
other on some types of devices that have multiple types of resources.
Additionally, some clk drivers already have their own separate
sync_state callback already defined.

Let's introduce support for allowing drivers and frameworks to add their
own sync_state callback via a new function dev_add_sync_state() so that
multiple sync_state callbacks can coexist.

Link: https://lore.kernel.org/linux-clk/CAPx+jO9JiV16ePLk59hTQzEMnA96Va6Ns4jqJbwyZ6oTT0AjXA@xxxxxxxxxxxxxx/
Signed-off-by: Brian Masney <bmasney@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4-6
---
 drivers/base/base.h    |  7 +++++++
 drivers/base/core.c    | 29 +++++++++++++++++++++++++++++
 include/linux/device.h | 11 +++++++++++
 3 files changed, 47 insertions(+)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index a5b7abc10ff0..339db4afbeb4 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -178,6 +178,8 @@ static inline bool dev_has_sync_state(struct device *dev)
 
 	if (!dev)
 		return false;
+	if (!list_empty(&dev->sync_state_list))
+		return true;
 	drv = READ_ONCE(dev->driver);
 	if (drv && drv->sync_state)
 		return true;
@@ -188,10 +190,15 @@ static inline bool dev_has_sync_state(struct device *dev)
 
 static inline void dev_sync_state(struct device *dev)
 {
+	struct sync_state_entry *entry;
+
 	if (dev->bus->sync_state)
 		dev->bus->sync_state(dev);
 	else if (dev->driver && dev->driver->sync_state)
 		dev->driver->sync_state(dev);
+
+	list_for_each_entry(entry, &dev->sync_state_list, node)
+		entry->fn(dev);
 }
 
 int driver_add_groups(const struct device_driver *drv,
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 4d026682944f..acc12f402dd3 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2612,6 +2612,7 @@ EXPORT_SYMBOL_GPL(device_show_string);
 static void device_release(struct kobject *kobj)
 {
 	struct device *dev = kobj_to_dev(kobj);
+	struct sync_state_entry *entry, *tmp;
 	struct device_private *p = dev->p;
 
 	/*
@@ -2625,6 +2626,11 @@ static void device_release(struct kobject *kobj)
 	 */
 	devres_release_all(dev);
 
+	list_for_each_entry_safe(entry, tmp, &dev->sync_state_list, node) {
+		list_del(&entry->node);
+		kfree(entry);
+	}
+
 	kfree(dev->dma_range_map);
 	kfree(dev->driver_override.name);
 
@@ -3239,12 +3245,35 @@ void device_initialize(struct device *dev)
 	INIT_LIST_HEAD(&dev->links.consumers);
 	INIT_LIST_HEAD(&dev->links.suppliers);
 	INIT_LIST_HEAD(&dev->links.defer_sync);
+	INIT_LIST_HEAD(&dev->sync_state_list);
 	dev->links.status = DL_DEV_NO_DRIVER;
 	dev_assign_dma_coherent(dev, dma_default_coherent);
 	swiotlb_dev_init(dev);
 }
 EXPORT_SYMBOL_GPL(device_initialize);
 
+int dev_add_sync_state(struct device *dev,
+			   void (*fn)(struct device *dev))
+{
+	struct sync_state_entry *entry;
+
+	if (!dev || !dev->driver)
+		return 0;
+
+	list_for_each_entry(entry, &dev->sync_state_list, node)
+		if (entry->fn == fn)
+			return 0;
+
+	entry = kmalloc_obj(*entry);
+	if (!entry)
+		return -ENOMEM;
+
+	entry->fn = fn;
+	list_add_tail(&entry->node, &dev->sync_state_list);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dev_add_sync_state);
+
 struct kobject *virtual_device_parent(void)
 {
 	static struct kobject *virtual_dir = NULL;
diff --git a/include/linux/device.h b/include/linux/device.h
index 7b2baffdd2f5..b7a3dd4b56ed 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -642,6 +642,8 @@ enum struct_device_flags {
  * @driver_override: Driver name to force a match.  Do not touch directly; use
  *		     device_set_driver_override() instead.
  * @links:	Links to suppliers and consumers of this device.
+ * @sync_state_list: List of sync_state callbacks added by subsystem
+ *		frameworks (e.g. clk, genpd) via dev_add_sync_state().
  * @power:	For device power management.
  *		See Documentation/driver-api/pm/devices.rst for details.
  * @pm_domain:	Provide callbacks that are executed during system suspend,
@@ -723,6 +725,7 @@ struct device {
 					 */
 
 	struct dev_links_info	links;
+	struct list_head	sync_state_list;
 	struct dev_pm_info	power;
 	struct dev_pm_domain	*pm_domain;
 
@@ -1137,6 +1140,14 @@ static inline int dev_set_drv_sync_state(struct device *dev,
 	return 0;
 }
 
+struct sync_state_entry {
+	struct list_head	node;
+	void			(*fn)(struct device *dev);
+};
+
+int dev_add_sync_state(struct device *dev,
+			   void (*fn)(struct device *dev));
+
 static inline void dev_set_removable(struct device *dev,
 				     enum device_removable removable)
 {

-- 
2.54.0