driver core: Expose device link details in sysfs

It's helpful to be able to look at device link details from sysfs. So,
expose it in sysfs.

Say device-A is supplier of device-B. These are the additional files
this patch would create:

/sys/class/devlink/device-A:device-B/
	auto_remove_on
	consumer/ -> .../device-B/
	runtime_pm
	status
	supplier/ -> .../device-A/
	sync_state_only

/sys/devices/.../device-A/
	consumer:device-B/ -> /sys/class/devlink/device-A:device-B/

/sys/devices/.../device-B/
	supplier:device-A/ -> /sys/class/devlink/device-A:device-B/

That way:
To get a list of all the device link in the system:
ls /sys/class/devlink/

To get the consumer names and links of a device:
ls -d /sys/devices/.../device-X/consumer:*

To get the supplier names and links of a device:
ls -d /sys/devices/.../device-X/supplier:*

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20200521191800.136035-2-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 30 insertions, 28 deletions

diff --git a/include/linux/device.h b/include/linux/device.h
index 9a62f7f43d55..efad96ea17a0 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -387,34 +387,6 @@ enum device_link_state {
 #define DL_FLAG_SYNC_STATE_ONLY		BIT(7)
 
 /**
- * struct device_link - Device link representation.
- * @supplier: The device on the supplier end of the link.
- * @s_node: Hook to the supplier device's list of links to consumers.
- * @consumer: The device on the consumer end of the link.
- * @c_node: Hook to the consumer device's list of links to suppliers.
- * @status: The state of the link (with respect to the presence of drivers).
- * @flags: Link flags.
- * @rpm_active: Whether or not the consumer device is runtime-PM-active.
- * @kref: Count repeated addition of the same link.
- * @rcu_head: An RCU head to use for deferred execution of SRCU callbacks.
- * @supplier_preactivated: Supplier has been made active before consumer probe.
- */
-struct device_link {
-	struct device *supplier;
-	struct list_head s_node;
-	struct device *consumer;
-	struct list_head c_node;
-	enum device_link_state status;
-	u32 flags;
-	refcount_t rpm_active;
-	struct kref kref;
-#ifdef CONFIG_SRCU
-	struct rcu_head rcu_head;
-#endif
-	bool supplier_preactivated; /* Owned by consumer probe. */
-};
-
-/**
  * enum dl_dev_state - Device driver presence tracking information.
  * @DL_DEV_NO_DRIVER: There is no driver attached to the device.
  * @DL_DEV_PROBING: A driver is probing.
@@ -624,6 +596,36 @@ struct device {
 #endif
 };
 
+/**
+ * struct device_link - Device link representation.
+ * @supplier: The device on the supplier end of the link.
+ * @s_node: Hook to the supplier device's list of links to consumers.
+ * @consumer: The device on the consumer end of the link.
+ * @c_node: Hook to the consumer device's list of links to suppliers.
+ * @link_dev: device used to expose link details in sysfs
+ * @status: The state of the link (with respect to the presence of drivers).
+ * @flags: Link flags.
+ * @rpm_active: Whether or not the consumer device is runtime-PM-active.
+ * @kref: Count repeated addition of the same link.
+ * @rcu_head: An RCU head to use for deferred execution of SRCU callbacks.
+ * @supplier_preactivated: Supplier has been made active before consumer probe.
+ */
+struct device_link {
+	struct device *supplier;
+	struct list_head s_node;
+	struct device *consumer;
+	struct list_head c_node;
+	struct device link_dev;
+	enum device_link_state status;
+	u32 flags;
+	refcount_t rpm_active;
+	struct kref kref;
+#ifdef CONFIG_SRCU
+	struct rcu_head rcu_head;
+#endif
+	bool supplier_preactivated; /* Owned by consumer probe. */
+};
+
 static inline struct device *kobj_to_dev(struct kobject *kobj)
 {
 	return container_of(kobj, struct device, kobj);