[PATCH 1/9] driver core: Enable suppliers to implement fine grained sync_state support

[Ulf Hansson]

The common sync_state support isn't fine grained enough for some types of
suppliers, like power domains for example. Especially when a supplier
provides multiple independent power domains, each with their own set of
consumers. In these cases we need to wait for all consumers for all the
provided power domains before invoking the supplier's ->sync_state().

To allow a more fine grained sync_state support to be implemented on per
supplier's driver basis, let's add a new optional callback. As soon as
there is an update worth to consider in regards to managing sync_state for
a supplier device, __device_links_queue_sync_state() invokes the callback.

Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
---
 drivers/base/core.c           | 7 ++++++-
 include/linux/device/driver.h | 7 +++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 791f9e444df8..a262714a83b6 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1106,7 +1106,9 @@ int device_links_check_suppliers(struct device *dev)
  * Queues a device for a sync_state() callback when the device links write lock
  * isn't held. This allows the sync_state() execution flow to use device links
  * APIs.  The caller must ensure this function is called with
- * device_links_write_lock() held.
+ * device_links_write_lock() held.  Note, if the optional queue_sync_state()
+ * callback has been assigned too, it gets called for every update to allowing a
+ * more fine grained support to be implemented on per supplier basis.
  *
  * This function does a get_device() to make sure the device is not freed while
  * on this list.
@@ -1126,6 +1128,9 @@ static void __device_links_queue_sync_state(struct device *dev,
 	if (dev->state_synced)
 		return;
 
+	if (dev->driver && dev->driver->queue_sync_state)
+		dev->driver->queue_sync_state(dev);
+
 	list_for_each_entry(link, &dev->links.consumers, s_node) {
 		if (!device_link_test(link, DL_FLAG_MANAGED))
 			continue;
diff --git a/include/linux/device/driver.h b/include/linux/device/driver.h
index bbc67ec513ed..bc9ae1cbe03c 100644
--- a/include/linux/device/driver.h
+++ b/include/linux/device/driver.h
@@ -68,6 +68,12 @@ enum probe_type {
  *		be called at late_initcall_sync level. If the device has
  *		consumers that are never bound to a driver, this function
  *		will never get called until they do.
+ * @queue_sync_state: Similar to the ->sync_state() callback, but called to
+ *		allow syncing device state to software state in a more fine
+ *		grained way. It is called when there is an updated state that
+ *		may be worth to consider for any of the consumers linked to
+ *		this device. If implemented, the ->sync_state() callback is
+ *		required too.
  * @remove:	Called when the device is removed from the system to
  *		unbind a device from this driver.
  * @shutdown:	Called at shut-down time to quiesce the device.
@@ -110,6 +116,7 @@ struct device_driver {
 
 	int (*probe) (struct device *dev);
 	void (*sync_state)(struct device *dev);
+	void (*queue_sync_state)(struct device *dev);
 	int (*remove) (struct device *dev);
 	void (*shutdown) (struct device *dev);
 	int (*suspend) (struct device *dev, pm_message_t state);
-- 
2.43.0