[PATCH 5.14 093/172] driver core: fw_devlink: Add support for FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD

Greg Kroah-Hartman
2021-10-04T13:38:48Z

From: Saravana Kannan <saravanak@google.com>

[ Upstream commit 5501765a02a6c324f78581e6bb8209d054fe13ae ]

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>
Link: https://lore.kernel.org/r/20210915170940.617415-3-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 8c77e14987d4..3d2fc70b9951 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1721,6 +1721,25 @@ 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