[PATCH v3 2/3] driver core: fw_devlink: Add support for FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD

[Saravana Kannan <saravanak@google.com>]

If a parent device is also a supplier to a child device, fw_devlink=on by
design delays the probe() of the child device until the probe() of the
parent finishes successfully.

However, some drivers of such parent devices (where parent is also a
supplier) expect the child device to finish probing successfully as soon as
they are added using device_add() and before the probe() of the parent
device has completed successfully. One example of such a case is discussed
in the link mentioned below.

Add a flag to make fw_devlink=on not enforce these supplier-consumer
relationships, so these drivers can continue working.

Link: https://lore.kernel.org/netdev/CAGETcx_uj0V4DChME-gy5HGKTYnxLBX=TH2rag29f_p=UcG+Tg@mail.gmail.com/
Fixes: ea718c699055 ("Revert "Revert "driver core: Set fw_devlink=on by default""")
Signed-off-by: Saravana Kannan <saravanak@google.com>
---
 drivers/base/core.c    | 19 +++++++++++++++++++
 include/linux/fwnode.h | 11 ++++++++---
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 316df6027093..21d4cb5d3767 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1722,6 +1722,25 @@ static int fw_devlink_create_devlink(struct device *con,
 	struct device *sup_dev;
 	int ret = 0;
 
+	/*
+	 * In some cases, a device P might also be a supplier to its child node
+	 * C. However, this would defer the probe of C until the probe of P
+	 * completes successfully. This is perfectly fine in the device driver
+	 * model. device_add() doesn't guarantee probe completion of the device
+	 * by the time it returns.
+	 *
+	 * However, there are a few drivers that assume C will finish probing
+	 * as soon as it's added and before P finishes probing. So, we provide
+	 * a flag to let fw_devlink know not to delay the probe of C until the
+	 * probe of P completes successfully.
+	 *
+	 * When such a flag is set, we can't create device links where P is the
+	 * supplier of C as that would delay the probe of C.
+	 */
+	if (sup_handle->flags & FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD &&
+	    fwnode_is_ancestor_of(sup_handle, con->fwnode))
+		return -EINVAL;
+
 	sup_dev = get_dev_from_fwnode(sup_handle);
 	if (sup_dev) {
 		/*
diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
index 59828516ebaf..9f4ad719bfe3 100644
--- a/include/linux/fwnode.h
+++ b/include/linux/fwnode.h
@@ -22,10 +22,15 @@ struct device;
  * LINKS_ADDED:	The fwnode has already be parsed to add fwnode links.
  * NOT_DEVICE:	The fwnode will never be populated as a struct device.
  * INITIALIZED: The hardware corresponding to fwnode has been initialized.
+ * NEEDS_CHILD_BOUND_ON_ADD: For this fwnode/device to probe successfully, its
+ *			     driver needs its child devices to be bound with
+ *			     their respective drivers as soon as they are
+ *			     added.
  */
-#define FWNODE_FLAG_LINKS_ADDED		BIT(0)
-#define FWNODE_FLAG_NOT_DEVICE		BIT(1)
-#define FWNODE_FLAG_INITIALIZED		BIT(2)
+#define FWNODE_FLAG_LINKS_ADDED			BIT(0)
+#define FWNODE_FLAG_NOT_DEVICE			BIT(1)
+#define FWNODE_FLAG_INITIALIZED			BIT(2)
+#define FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD	BIT(3)
 
 struct fwnode_handle {
 	struct fwnode_handle *secondary;
-- 
2.33.0.309.g3052b89438-goog