linux-kernel - [PATCH v1] driver core: Add device links from fwnode only for the primary device

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Date:   Fri, 20 Mar 2020 21:54:48 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Saravana Kannan <saravanak@...gle.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org
Subject: [PATCH v1] driver core: Add device links from fwnode only for the
 primary device

Sometimes, more than one (generally two) device can point to the same
fwnode.  However, only one device is set as the fwnode's device
(fwnode->dev) and can be looked up from the fwnode.

Typically, only one of these devices actually have a driver and actually
probe. If we create device links for all these devices, then the
suppliers' of these devices (with the same fwnode) will never get a
sync_state() call because one of their consumer devices will never probe
(because they don't have a driver).

So, create device links only for the device that is considered as the
fwnode's device.

One such example of this is the PCI bridge platform_device and the
corresponding pci_bus device. Both these devices will have the same
fwnode. It's the platform_device that is registered first and is set as
the fwnode's device. Also the platform_device is the one that actually
probes. Without this patch none of the suppliers of a PCI bridge
platform_device would get a sync_state() callback.

Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-pci@...r.kernel.org
Signed-off-by: Saravana Kannan <saravanak@...gle.com>
---
 drivers/base/core.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index fc6a60998cd6..5e3cc1651c78 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2404,6 +2404,7 @@ int device_add(struct device *dev)
 	struct class_interface *class_intf;
 	int error = -EINVAL, fw_ret;
 	struct kobject *glue_dir = NULL;
+	bool is_fwnode_dev = false;

 	dev = get_device(dev);
 	if (!dev)
@@ -2501,8 +2502,10 @@ int device_add(struct device *dev)

 	kobject_uevent(&dev->kobj, KOBJ_ADD);

-	if (dev->fwnode && !dev->fwnode->dev)
+	if (dev->fwnode && !dev->fwnode->dev) {
 		dev->fwnode->dev = dev;
+		is_fwnode_dev = true;
+	}

 	/*
 	 * Check if any of the other devices (consumers) have been waiting for
@@ -2518,7 +2521,8 @@ int device_add(struct device *dev)
 	 */
 	device_link_add_missing_supplier_links();

-	if (fw_devlink_flags && fwnode_has_op(dev->fwnode, add_links)) {
+	if (fw_devlink_flags && is_fwnode_dev &&
+	    fwnode_has_op(dev->fwnode, add_links)) {
 		fw_ret = fwnode_call_int_op(dev->fwnode, add_links, dev);
 		if (fw_ret == -ENODEV)
 			device_link_wait_for_mandatory_supplier(dev);
-- 
2.25.1.696.g5e7596f4ac-goog