[PATCH RFC net-next 08/13] dpll: Enhance and consolidate reference counting logic

[Ivan Vecera <ivecera@redhat.com>]

Refactor the reference counting mechanism for DPLL devices and pins to
improve consistency and prevent potential lifetime issues.

Introduce internal helpers __dpll_{device,pin}_{hold,put}() to
centralize reference management.

Update the internal XArray reference helpers (dpll_xa_ref_*) to
automatically grab a reference to the target object when it is added to
a list, and release it when removed. This ensures that objects linked
internally (e.g., pins referenced by parent pins) are properly kept
alive without relying on the caller to manually manage the count.

Consequently, remove the now redundant manual `refcount_inc/dec` calls
in dpll_pin_on_pin_{,un}register()`, as ownership is now correctly handled
by the dpll_xa_ref_* functions.

Additionally, ensure that dpll_device_{,un}register()` takes/releases
a reference to the device, ensuring the device object remains valid for
the duration of its registration.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
---
 drivers/dpll/dpll_core.c | 74 +++++++++++++++++++++++++++-------------
 1 file changed, 50 insertions(+), 24 deletions(-)

diff --git a/drivers/dpll/dpll_core.c b/drivers/dpll/dpll_core.c
index 79f60e0de27ac..f4a4e17fb9b6c 100644
--- a/drivers/dpll/dpll_core.c
+++ b/drivers/dpll/dpll_core.c
@@ -83,6 +83,45 @@ void dpll_pin_notify(struct dpll_pin *pin, unsigned long action)
 	call_dpll_notifiers(action, &info);
 }
 
+static void __dpll_device_hold(struct dpll_device *dpll)
+{
+	refcount_inc(&dpll->refcount);
+}
+
+static void __dpll_device_put(struct dpll_device *dpll)
+{
+	if (refcount_dec_and_test(&dpll->refcount)) {
+		ASSERT_DPLL_NOT_REGISTERED(dpll);
+		WARN_ON_ONCE(!xa_empty(&dpll->pin_refs));
+		xa_destroy(&dpll->pin_refs);
+		xa_erase(&dpll_device_xa, dpll->id);
+		WARN_ON(!list_empty(&dpll->registration_list));
+		kfree(dpll);
+	}
+}
+
+static void __dpll_pin_hold(struct dpll_pin *pin)
+{
+	refcount_inc(&pin->refcount);
+}
+
+static void dpll_pin_idx_free(u32 pin_idx);
+static void dpll_pin_prop_free(struct dpll_pin_properties *prop);
+
+static void __dpll_pin_put(struct dpll_pin *pin)
+{
+	if (refcount_dec_and_test(&pin->refcount)) {
+		xa_erase(&dpll_pin_xa, pin->id);
+		xa_destroy(&pin->dpll_refs);
+		xa_destroy(&pin->parent_refs);
+		xa_destroy(&pin->ref_sync_pins);
+		dpll_pin_prop_free(&pin->prop);
+		fwnode_handle_put(pin->fwnode);
+		dpll_pin_idx_free(pin->pin_idx);
+		kfree_rcu(pin, rcu);
+	}
+}
+
 struct dpll_device *dpll_device_get_by_id(int id)
 {
 	if (xa_get_mark(&dpll_device_xa, id, DPLL_REGISTERED))
@@ -154,6 +193,7 @@ dpll_xa_ref_pin_add(struct xarray *xa_pins, struct dpll_pin *pin,
 	reg->ops = ops;
 	reg->priv = priv;
 	reg->cookie = cookie;
+	__dpll_pin_hold(pin);
 	if (ref_exists)
 		refcount_inc(&ref->refcount);
 	list_add_tail(&reg->list, &ref->registration_list);
@@ -176,6 +216,7 @@ static int dpll_xa_ref_pin_del(struct xarray *xa_pins, struct dpll_pin *pin,
 		if (WARN_ON(!reg))
 			return -EINVAL;
 		list_del(&reg->list);
+		__dpll_pin_put(pin);
 		kfree(reg);
 		if (refcount_dec_and_test(&ref->refcount)) {
 			xa_erase(xa_pins, i);
@@ -235,6 +276,7 @@ dpll_xa_ref_dpll_add(struct xarray *xa_dplls, struct dpll_device *dpll,
 	reg->ops = ops;
 	reg->priv = priv;
 	reg->cookie = cookie;
+	__dpll_device_hold(dpll);
 	if (ref_exists)
 		refcount_inc(&ref->refcount);
 	list_add_tail(&reg->list, &ref->registration_list);
@@ -257,6 +299,7 @@ dpll_xa_ref_dpll_del(struct xarray *xa_dplls, struct dpll_device *dpll,
 		if (WARN_ON(!reg))
 			return;
 		list_del(&reg->list);
+		__dpll_device_put(dpll);
 		kfree(reg);
 		if (refcount_dec_and_test(&ref->refcount)) {
 			xa_erase(xa_dplls, i);
@@ -327,8 +370,8 @@ dpll_device_get(u64 clock_id, u32 device_idx, struct module *module)
 		if (dpll->clock_id == clock_id &&
 		    dpll->device_idx == device_idx &&
 		    dpll->module == module) {
+			__dpll_device_hold(dpll);
 			ret = dpll;
-			refcount_inc(&ret->refcount);
 			break;
 		}
 	}
@@ -351,14 +394,7 @@ EXPORT_SYMBOL_GPL(dpll_device_get);
 void dpll_device_put(struct dpll_device *dpll)
 {
 	mutex_lock(&dpll_lock);
-	if (refcount_dec_and_test(&dpll->refcount)) {
-		ASSERT_DPLL_NOT_REGISTERED(dpll);
-		WARN_ON_ONCE(!xa_empty(&dpll->pin_refs));
-		xa_destroy(&dpll->pin_refs);
-		xa_erase(&dpll_device_xa, dpll->id);
-		WARN_ON(!list_empty(&dpll->registration_list));
-		kfree(dpll);
-	}
+	__dpll_device_put(dpll);
 	mutex_unlock(&dpll_lock);
 }
 EXPORT_SYMBOL_GPL(dpll_device_put);
@@ -420,6 +456,7 @@ int dpll_device_register(struct dpll_device *dpll, enum dpll_type type,
 	reg->ops = ops;
 	reg->priv = priv;
 	dpll->type = type;
+	__dpll_device_hold(dpll);
 	first_registration = list_empty(&dpll->registration_list);
 	list_add_tail(&reg->list, &dpll->registration_list);
 	if (!first_registration) {
@@ -459,6 +496,7 @@ void dpll_device_unregister(struct dpll_device *dpll,
 		return;
 	}
 	list_del(&reg->list);
+	__dpll_device_put(dpll);
 	kfree(reg);
 
 	if (!list_empty(&dpll->registration_list)) {
@@ -675,8 +713,8 @@ dpll_pin_get(u64 clock_id, u32 pin_idx, struct module *module,
 		    pos->pin_idx == pin_idx &&
 		    pos->module == module &&
 		    pos->fwnode == fwnode) {
+			__dpll_pin_hold(pos);
 			ret = pos;
-			refcount_inc(&ret->refcount);
 			break;
 		}
 	}
@@ -699,16 +737,7 @@ EXPORT_SYMBOL_GPL(dpll_pin_get);
 void dpll_pin_put(struct dpll_pin *pin)
 {
 	mutex_lock(&dpll_lock);
-	if (refcount_dec_and_test(&pin->refcount)) {
-		xa_erase(&dpll_pin_xa, pin->id);
-		xa_destroy(&pin->dpll_refs);
-		xa_destroy(&pin->parent_refs);
-		xa_destroy(&pin->ref_sync_pins);
-		dpll_pin_prop_free(&pin->prop);
-		fwnode_handle_put(pin->fwnode);
-		dpll_pin_idx_free(pin->pin_idx);
-		kfree_rcu(pin, rcu);
-	}
+	__dpll_pin_put(pin);
 	mutex_unlock(&dpll_lock);
 }
 EXPORT_SYMBOL_GPL(dpll_pin_put);
@@ -733,8 +762,8 @@ struct dpll_pin *fwnode_dpll_pin_find(struct fwnode_handle *fwnode)
 	mutex_lock(&dpll_lock);
 	xa_for_each(&dpll_pin_xa, index, pin) {
 		if (pin->fwnode == fwnode) {
+			__dpll_pin_hold(pin);
 			ret = pin;
-			refcount_inc(&ret->refcount);
 			break;
 		}
 	}
@@ -886,7 +915,6 @@ int dpll_pin_on_pin_register(struct dpll_pin *parent, struct dpll_pin *pin,
 	ret = dpll_xa_ref_pin_add(&pin->parent_refs, parent, ops, priv, pin);
 	if (ret)
 		goto unlock;
-	refcount_inc(&pin->refcount);
 	xa_for_each(&parent->dpll_refs, i, ref) {
 		ret = __dpll_pin_register(ref->dpll, pin, ops, priv, parent);
 		if (ret) {
@@ -906,7 +934,6 @@ int dpll_pin_on_pin_register(struct dpll_pin *parent, struct dpll_pin *pin,
 					      parent);
 			dpll_pin_delete_ntf(pin);
 		}
-	refcount_dec(&pin->refcount);
 	dpll_xa_ref_pin_del(&pin->parent_refs, parent, ops, priv, pin);
 unlock:
 	mutex_unlock(&dpll_lock);
@@ -933,7 +960,6 @@ void dpll_pin_on_pin_unregister(struct dpll_pin *parent, struct dpll_pin *pin,
 	mutex_lock(&dpll_lock);
 	dpll_pin_delete_ntf(pin);
 	dpll_xa_ref_pin_del(&pin->parent_refs, parent, ops, priv, pin);
-	refcount_dec(&pin->refcount);
 	xa_for_each(&pin->dpll_refs, i, ref)
 		__dpll_pin_unregister(ref->dpll, pin, ops, priv, parent);
 	mutex_unlock(&dpll_lock);
-- 
2.51.2