When consumer devices are added, they might not have a supplier device
to link to despite needing mandatory resources/functionality from one
or more suppliers. Add a waiting_for_suppliers list to track such
consumers and add helper functions to manage the list.
Marking/unmarking a consumer device as waiting for suppliers is
generally expected to be done by the entity that's creating the
device.
Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>
---
drivers/base/core.c | 67 ++++++++++++++++++++++++++++++++++++++++++
include/linux/device.h | 5 ++++
2 files changed, 72 insertions(+)
diff --git a/drivers/base/core.c b/drivers/base/core.c
index fd7511e04e62..9ab6782dda1c 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -44,6 +44,8 @@ early_param("sysfs.deprecated", sysfs_deprecated_setup);
#endif
/* Device links support. */
+static LIST_HEAD(wait_for_suppliers);
+static DEFINE_MUTEX(wfs_lock);
#ifdef CONFIG_SRCU
static DEFINE_MUTEX(device_links_lock);
@@ -401,6 +403,53 @@ struct device_link *device_link_add(struct device *consumer,
}
EXPORT_SYMBOL_GPL(device_link_add);
+/**
+ * device_link_wait_for_supplier - Mark device as waiting for supplier
+ * @consumer: Consumer device
+ *
+ * Marks the consumer device as waiting for suppliers to become available. The
+ * consumer device will never be probed until it's unmarked as waiting for
+ * suppliers. The caller is responsible for adding the link to the supplier
+ * once the supplier device is present.
+ *
+ * This function is NOT meant to be called from the probe function of the
+ * consumer but rather from code that creates the consumer device.
+ */
+void device_link_wait_for_supplier(struct device *consumer)
+{
+ mutex_lock(&wfs_lock);
+ list_add_tail(&consumer->links.needs_suppliers, &wait_for_suppliers);
+ mutex_unlock(&wfs_lock);
+}
+
+/**
+ * device_link_check_waiting_consumers - Try to unmark waiting consumers
+ * @add_suppliers: Callback function to add suppliers to waiting consumer
+ *
+ * Loops through all consumers waiting on suppliers and tries to add all their
+ * supplier links. If that succeeds, the consumer device is unmarked as waiting
+ * for suppliers. Otherwise, they are left marked as waiting on suppliers,
+ *
+ * The add_suppliers callback is expected to return 0 if it has found and added
+ * all the supplier links for the consumer device. It should return an error if
+ * it isn't able to do so.
+ *
+ * The caller of device_link_wait_for_supplier() is expected to call this once
+ * it's aware of potential suppliers becoming available.
+ */
+void device_link_check_waiting_consumers(
+ int (*add_suppliers)(struct device *consumer))
+{
+ struct device *dev, *tmp;
+
+ mutex_lock(&wfs_lock);
+ list_for_each_entry_safe(dev, tmp, &wait_for_suppliers,
+ links.needs_suppliers)
+ if (!add_suppliers(dev))
+ list_del_init(&dev->links.needs_suppliers);
+ mutex_unlock(&wfs_lock);
+}
+
static void device_link_free(struct device_link *link)
{
while (refcount_dec_not_one(&link->rpm_active))
@@ -535,6 +584,19 @@ int device_links_check_suppliers(struct device *dev)
struct device_link *link;
int ret = 0;
+ /*
+ * If a device is waiting for one or more suppliers (in
+ * wait_for_suppliers list), it is not ready to probe yet. So just
+ * return -EPROBE_DEFER without having to check the links with existing
+ * suppliers.
+ */
+ mutex_lock(&wfs_lock);
+ if (!list_empty(&dev->links.needs_suppliers)) {
+ mutex_unlock(&wfs_lock);
+ return -EPROBE_DEFER;
+ }
+ mutex_unlock(&wfs_lock);
+
device_links_write_lock();
list_for_each_entry(link, &dev->links.suppliers, c_node) {
@@ -812,6 +874,10 @@ static void device_links_purge(struct device *dev)
{
struct device_link *link, *ln;
+ mutex_lock(&wfs_lock);
+ list_del(&dev->links.needs_suppliers);
+ mutex_unlock(&wfs_lock);
+
/*
* Delete all of the remaining links from this device to any other
* devices (either consumers or suppliers).
@@ -1673,6 +1739,7 @@ void device_initialize(struct device *dev)
#endif
INIT_LIST_HEAD(&dev->links.consumers);
INIT_LIST_HEAD(&dev->links.suppliers);
+ INIT_LIST_HEAD(&dev->links.needs_suppliers);
dev->links.status = DL_DEV_NO_DRIVER;
}
EXPORT_SYMBOL_GPL(device_initialize);
diff --git a/include/linux/device.h b/include/linux/device.h
index e85264fb6616..4e71e5386aae 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -887,11 +887,13 @@ enum dl_dev_state {
* struct dev_links_info - Device data related to device links.
* @suppliers: List of links to supplier devices.
* @consumers: List of links to consumer devices.
+ * @needs_suppliers: Hook to global list of devices waiting for suppliers.
* @status: Driver status information.
*/
struct dev_links_info {
struct list_head suppliers;
struct list_head consumers;
+ struct list_head needs_suppliers;
enum dl_dev_state status;
};
@@ -1395,6 +1397,9 @@ struct device_link *device_link_add(struct device *consumer,
struct device *supplier, u32 flags);
void device_link_del(struct device_link *link);
void device_link_remove(void *consumer, struct device *supplier);
+void device_link_wait_for_supplier(struct device *consumer);
+void device_link_check_waiting_consumers(
+ int (*add_suppliers)(struct device *consumer));
#ifndef dev_fmt
#define dev_fmt(fmt) fmt
--
2.22.0.rc1.257.g3120a18244-goog
