[PATCH v3 3/3] driver core: Add waiting_for_supplier sysfs file for devices

[Saravana Kannan <saravanak@google.com>]

This would be useful to check if a device is not probing because it's
waiting for a supplier to be added and then linked to before it can
probe.

To reduce sysfs clutter, this file is added only if it can ever be 1.
So, if fw_devlink is disabled or set to permissive, this file is not
added. Also, this file is removed once the device probes as it's no
longer relevant.

Signed-off-by: Saravana Kannan <saravanak@google.com>
---
 .../sysfs-devices-waiting_for_supplier        | 17 ++++++++++++
 drivers/base/core.c                           | 26 +++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-devices-waiting_for_supplier

diff --git a/Documentation/ABI/testing/sysfs-devices-waiting_for_supplier b/Documentation/ABI/testing/sysfs-devices-waiting_for_supplier
new file mode 100644
index 000000000000..59d073d20db6
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-waiting_for_supplier
@@ -0,0 +1,17 @@
+What:		/sys/devices/.../waiting_for_supplier
+Date:		May 2020
+Contact:	Saravana Kannan <saravanak@google.com>
+Description:
+		The /sys/devices/.../waiting_for_supplier attribute is only
+		present when fw_devlink kernel command line option is enabled
+		and is set to something stricter than "permissive".  It is
+		removed once a device probes successfully (because the
+		information is no longer relevant). The number read from it (0
+		or 1) reflects whether the device is waiting for one or more
+		suppliers to be added and then linked to using device links
+		before the device can probe.
+
+		A value of 0 means the device is not waiting for any suppliers
+		to be added before it can probe.  A value of 1 means the device
+		is waiting for one or more suppliers to be added before it can
+		probe.
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 81c8ef088d3a..dfd4e94ef790 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1033,6 +1033,22 @@ static void device_link_drop_managed(struct device_link *link)
 	kref_put(&link->kref, __device_link_del);
 }
 
+static ssize_t waiting_for_supplier_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	bool val;
+
+	device_lock(dev);
+	mutex_lock(&wfs_lock);
+	val = !list_empty(&dev->links.needs_suppliers)
+	      && dev->links.need_for_probe;
+	mutex_unlock(&wfs_lock);
+	device_unlock(dev);
+	return sprintf(buf, "%u\n", val);
+}
+static DEVICE_ATTR_RO(waiting_for_supplier);
+
 /**
  * device_links_driver_bound - Update device links after probing its driver.
  * @dev: Device to update the links for.
@@ -1057,6 +1073,7 @@ void device_links_driver_bound(struct device *dev)
 	mutex_lock(&wfs_lock);
 	list_del_init(&dev->links.needs_suppliers);
 	mutex_unlock(&wfs_lock);
+	device_remove_file(dev, &dev_attr_waiting_for_supplier);
 
 	device_links_write_lock();
 
@@ -2126,8 +2143,16 @@ static int device_add_attrs(struct device *dev)
 			goto err_remove_dev_groups;
 	}
 
+	if (fw_devlink_flags && !fw_devlink_is_permissive()) {
+		error = device_create_file(dev, &dev_attr_waiting_for_supplier);
+		if (error)
+			goto err_remove_dev_online;
+	}
+
 	return 0;
 
+ err_remove_dev_online:
+	device_remove_file(dev, &dev_attr_online);
  err_remove_dev_groups:
 	device_remove_groups(dev, dev->groups);
  err_remove_type_groups:
@@ -2145,6 +2170,7 @@ static void device_remove_attrs(struct device *dev)
 	struct class *class = dev->class;
 	const struct device_type *type = dev->type;
 
+	device_remove_file(dev, &dev_attr_waiting_for_supplier);
 	device_remove_file(dev, &dev_attr_online);
 	device_remove_groups(dev, dev->groups);
 
-- 
2.27.0.rc0.183.gde8f92d652-goog