[PATCH v2 01/11] driver core: fw_devlink: Don't purge child fwnode's consumer links

Saravana Kannan
2023-01-27T00:12:11Z

When a device X is bound successfully to a driver, if it has a child
firmware node Y that doesn't have a struct device created by then, we
delete fwnode links where the child firmware node Y is the supplier. We
did this to avoid blocking the consumers of the child firmware node Y
from deferring probe indefinitely.

While that a step in the right direction, it's better to make the
consumers of the child firmware node Y to be consumers of the device X
because device X is probably implementing whatever functionality is
represented by child firmware node Y. By doing this, we capture the
device dependencies more accurately and ensure better
probe/suspend/resume ordering.

Signed-off-by: Saravana Kannan <saravanak@google.com>
---
drivers/base/core.c | 97 ++++++++++++++++++++++++++++++++++++---------
1 file changed, 79 insertions(+), 18 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index a3e14143ec0c..b6d98cc82f26 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -54,11 +54,12 @@ static LIST_HEAD(deferred_sync);
static unsigned int defer_sync_state_count = 1;
static DEFINE_MUTEX(fwnode_link_lock);
static bool fw_devlink_is_permissive(void);
+static void __fw_devlink_link_to_consumers(struct device *dev);
static bool fw_devlink_drv_reg_done;
static bool fw_devlink_best_effort;

/**
- * fwnode_link_add - Create a link between two fwnode_handles.
+ * __fwnode_link_add - Create a link between two fwnode_handles.
* @con: Consumer end of the link.
* @sup: Supplier end of the link.
*
@@ -74,22 +75,18 @@ static bool fw_devlink_best_effort;
* Attempts to create duplicate links between the same pair of fwnode handles
* are ignored and there is no reference counting.
*/
-int fwnode_link_add(struct fwnode_handle *con, struct fwnode_handle *sup)
+static int __fwnode_link_add(struct fwnode_handle *con,
+ struct fwnode_handle *sup)
{
struct fwnode_link *link;
- int ret = 0;
-
- mutex_lock(&fwnode_link_lock);

list_for_each_entry(link, &sup->consumers, s_hook)
if (link->consumer == con)
- goto out;
+ return 0;

link = kzalloc(sizeof(*link), GFP_KERNEL);
- if (!link) {
- ret = -ENOMEM;
- goto out;
- }
+ if (!link)
+ return -ENOMEM;

link->supplier = sup;
INIT_LIST_HEAD(&link->s_hook);
@@ -100,9 +97,17 @@ int fwnode_link_add(struct fwnode_handle *con, struct fwnode_handle *sup)
list_add(&link->c_hook, &con->suppliers);
pr_debug("%pfwP Linked as a fwnode consumer to %pfwP\n",
con, sup);
-out:
- mutex_unlock(&fwnode_link_lock);

+ return 0;
+}
+
+int fwnode_link_add(struct fwnode_handle *con, struct fwnode_handle *sup)
+{
+ int ret = 0;
+
+ mutex_lock(&fwnode_link_lock);
+ ret = __fwnode_link_add(con, sup);
+ mutex_unlock(&fwnode_link_lock);
return ret;
}

@@ -181,6 +186,51 @@ void fw_devlink_purge_absent_suppliers(struct fwnode_handle *fwnode)
}
EXPORT_SYMBOL_GPL(fw_devlink_purge_absent_suppliers);

+/**
+ * __fwnode_links_move_consumers - Move consumer from @from to @to fwnode_handle
+ * @from: move consumers away from this fwnode
+ * @to: move consumers to this fwnode
+ *
+ * Move all consumer links from @from fwnode to @to fwnode.
+ */
+static void __fwnode_links_move_consumers(struct fwnode_handle *from,
+ struct fwnode_handle *to)
+{
+ struct fwnode_link *link, *tmp;
+
+ list_for_each_entry_safe(link, tmp, &from->consumers, s_hook) {
+ __fwnode_link_add(link->consumer, to);
+ __fwnode_link_del(link);
+ }
+}
+
+/**
+ * __fw_devlink_pickup_dangling_consumers - Pick up dangling consumers
+ * @fwnode: fwnode from which to pick up dangling consumers
+ * @new_sup: fwnode of new supplier
+ *
+ * If the @fwnode has a corresponding struct device and the device supports
+ * probing (that is, added to a bus), then we want to let fw_devlink create
+ * MANAGED device links to this device, so leave @fwnode and its descendant's
+ * fwnode links alone.
+ *
+ * Otherwise, move its consumers to the new supplier @new_sup.
+ */
+static void __fw_devlink_pickup_dangling_consumers(struct fwnode_handle *fwnode,
+ struct fwnode_handle *new_sup)
+{
+ struct fwnode_handle *child;
+
+ if (fwnode->dev && fwnode->dev->bus)
+ return;
+
+ fwnode->flags |= FWNODE_FLAG_NOT_DEVICE;
+ __fwnode_links_move_consumers(fwnode, new_sup);
+
+ fwnode_for_each_available_child_node(fwnode, child)
+ __fw_devlink_pickup_dangling_consumers(child, new_sup);
+}
+
#ifdef CONFIG_SRCU
static DEFINE_MUTEX(device_links_lock);
DEFINE_STATIC_SRCU(device_links_srcu);
@@ -1267,16 +1317,23 @@ void device_links_driver_bound(struct device *dev)
* them. So, fw_devlink no longer needs to create device links to any
* of the device's suppliers.
*
- * Also, if a child firmware node of this bound device is not added as
- * a device by now, assume it is never going to be added and make sure
- * other devices don't defer probe indefinitely by waiting for such a
- * child device.
+ * Also, if a child firmware node of this bound device is not added as a
+ * device by now, assume it is never going to be added. Make this bound
+ * device the fallback supplier to the dangling consumers of the child
+ * firmware node because this bound device is probably implementing the
+ * child firmware node functionality and we don't want the dangling
+ * consumers to defer probe indefinitely waiting for a device for the
+ * child firmware node.
*/
if (dev->fwnode && dev->fwnode->dev == dev) {
struct fwnode_handle *child;
fwnode_links_purge_suppliers(dev->fwnode);
+ mutex_lock(&fwnode_link_lock);
fwnode_for_each_available_child_node(dev->fwnode, child)
- fw_devlink_purge_absent_suppliers(child);
+ __fw_devlink_pickup_dangling_consumers(child,
+ dev->fwnode);
+ __fw_devlink_link_to_consumers(dev);
+ mutex_unlock(&fwnode_link_lock);
}
device_remove_file(dev, &dev_attr_waiting_for_supplier);

@@ -1855,7 +1912,11 @@ static int fw_devlink_create_devlink(struct device *con,
fwnode_is_ancestor_of(sup_handle, con->fwnode))
return -EINVAL;

- sup_dev = get_dev_from_fwnode(sup_handle);
+ if (sup_handle->flags & FWNODE_FLAG_NOT_DEVICE)
+ sup_dev = fwnode_get_next_parent_dev(sup_handle);
+ else
+ sup_dev = get_dev_from_fwnode(sup_handle);
+
if (sup_dev) {
/*
* If it's one of those drivers that don't actually bind to
--
2.39.1.456.gfc5497dd1b-goog