[PATCH v2 06/11] driver core: fw_devlink: Allow marking a fwnode link as being part of a cycle

Saravana Kannan
2023-01-27T00:12:36Z

To improve detection and handling of dependency cycles, we need to be
able to mark fwnode links as being part of cycles. fwnode links marked
as being part of a cycle should not block their consumers from probing.

Fixes: 2de9d8e0d2fe ("driver core: fw_devlink: Improve handling of cyclic dependencies")
Signed-off-by: Saravana Kannan <saravanak@google.com>
---
drivers/base/core.c | 41 +++++++++++++++++++++++++++++++++++------
include/linux/fwnode.h | 11 ++++++++++-
2 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index e5390b09a02f..82b29e9070bf 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -126,6 +126,19 @@ static void __fwnode_link_del(struct fwnode_link *link)
kfree(link);
}

+/**
+ * __fwnode_link_cycle - Mark a fwnode link as being part of a cycle.
+ * @link: the fwnode_link to be marked
+ *
+ * The fwnode_link_lock needs to be held when this function is called.
+ */
+static void __fwnode_link_cycle(struct fwnode_link *link)
+{
+ pr_debug("%pfwf: Relaxing link with %pfwf\n",
+ link->consumer, link->supplier);
+ link->flags |= FWLINK_FLAG_CYCLE;
+}
+
/**
* fwnode_links_purge_suppliers - Delete all supplier links of fwnode_handle.
* @fwnode: fwnode whose supplier links need to be deleted
@@ -1041,6 +1054,23 @@ static bool dev_is_best_effort(struct device *dev)
(dev->fwnode && (dev->fwnode->flags & FWNODE_FLAG_BEST_EFFORT));
}

+static struct fwnode_handle *fwnode_links_check_suppliers(
+ struct fwnode_handle *fwnode)
+{
+ struct fwnode_link *link;
+
+ if (!fwnode || fw_devlink_is_permissive())
+ return NULL;
+
+ list_for_each_entry(link, &fwnode->suppliers, c_hook) {
+ if (link->flags & FWLINK_FLAG_CYCLE)
+ continue;
+ return link->supplier;
+ }
+
+ return NULL;
+}
+
/**
* device_links_check_suppliers - Check presence of supplier drivers.
* @dev: Consumer device.
@@ -1068,11 +1098,8 @@ int device_links_check_suppliers(struct device *dev)
* probe.
*/
mutex_lock(&fwnode_link_lock);
- if (dev->fwnode && !list_empty(&dev->fwnode->suppliers) &&
- !fw_devlink_is_permissive()) {
- sup_fw = list_first_entry(&dev->fwnode->suppliers,
- struct fwnode_link,
- c_hook)->supplier;
+ sup_fw = fwnode_links_check_suppliers(dev->fwnode);
+ if (sup_fw) {
if (!dev_is_best_effort(dev)) {
fwnode_ret = -EPROBE_DEFER;
dev_err_probe(dev, -EPROBE_DEFER,
@@ -1261,7 +1288,9 @@ static ssize_t waiting_for_supplier_show(struct device *dev,
bool val;

device_lock(dev);
- val = !list_empty(&dev->fwnode->suppliers);
+ mutex_lock(&fwnode_link_lock);
+ val = !!fwnode_links_check_suppliers(dev->fwnode);
+ mutex_unlock(&fwnode_link_lock);
device_unlock(dev);
return sysfs_emit(buf, "%u\n", val);
}
diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
index 89b9bdfca925..fdf2ee0285b7 100644
--- a/include/linux/fwnode.h
+++ b/include/linux/fwnode.h
@@ -18,7 +18,7 @@ struct fwnode_operations;
struct device;

/*
- * fwnode link flags
+ * fwnode flags
*
* LINKS_ADDED: The fwnode has already be parsed to add fwnode links.
* NOT_DEVICE: The fwnode will never be populated as a struct device.
@@ -36,6 +36,7 @@ struct device;
#define FWNODE_FLAG_INITIALIZED BIT(2)
#define FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD BIT(3)
#define FWNODE_FLAG_BEST_EFFORT BIT(4)
+#define FWNODE_FLAG_VISITED BIT(5)

struct fwnode_handle {
struct fwnode_handle *secondary;
@@ -46,11 +47,19 @@ struct fwnode_handle {
u8 flags;
};

+/*
+ * fwnode link flags
+ *
+ * CYCLE: The fwnode link is part of a cycle. Don't defer probe.
+ */
+#define FWLINK_FLAG_CYCLE BIT(0)
+
struct fwnode_link {
struct fwnode_handle *supplier;
struct list_head s_hook;
struct fwnode_handle *consumer;
struct list_head c_hook;
+ u8 flags;
};

/**
--
2.39.1.456.gfc5497dd1b-goog