[PATCH 1/1] device core: Add flag to autoremove device link on supplier unbind

[Vivek Gautam <vivek.gautam@codeaurora.org>]

When using the device links without the consumers or
suppliers maintaining pointers to these links, a flag can
help in autoremoving the links on supplier driver unbind.
We remove these links only when the supplier's link to its
consumers has gone in DL_STATE_SUPPLIER_UNBIND state.

Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
Suggested-by: Lukas Wunner <lukas@wunner.de>
---

Lukas, as suggested in the thread [1] this change adds additional flag
to autoremove device links on supplier unbind.
For arm-smmu, we want to _not_ keep references to the device links
added between arm-smmu, and consumer devices.
Robin also pointed to [2] the need to autoremove the device link on
supplier unbind rather than consumer unbind.

[1] https://lkml.org/lkml/2018/3/14/390
[2] https://lkml.org/lkml/2018/5/21/381

 drivers/base/core.c    | 10 ++++++++++
 include/linux/device.h |  2 ++
 2 files changed, 12 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index b610816eb887..52c7222bb3c4 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -490,6 +490,16 @@ void device_links_driver_cleanup(struct device *dev)
 
 		WARN_ON(link->flags & DL_FLAG_AUTOREMOVE);
 		WARN_ON(link->status != DL_STATE_SUPPLIER_UNBIND);
+
+		/*
+		 * autoremove the links between this @dev and its consumer
+		 * devices that are not active, i.e. where the link state
+		 * has moved to DL_STATE_SUPPLIER_UNBIND.
+		 */
+		if (link->status == DL_STATE_SUPPLIER_UNBIND &&
+		    link->flags & DL_FLAG_AUTOREMOVE_S)
+			kref_put(&link->kref, __device_link_del);
+
 		WRITE_ONCE(link->status, DL_STATE_DORMANT);
 	}
 
diff --git a/include/linux/device.h b/include/linux/device.h
index 477956990f5e..6033bf58453d 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -779,11 +779,13 @@ enum device_link_state {
  * AUTOREMOVE: Remove this link automatically on consumer driver unbind.
  * PM_RUNTIME: If set, the runtime PM framework will use this link.
  * RPM_ACTIVE: Run pm_runtime_get_sync() on the supplier during link creation.
+ * AUTOREMOVE_S: Remove this link automatically on supplier driver unbind.
  */
 #define DL_FLAG_STATELESS	BIT(0)
 #define DL_FLAG_AUTOREMOVE	BIT(1)
 #define DL_FLAG_PM_RUNTIME	BIT(2)
 #define DL_FLAG_RPM_ACTIVE	BIT(3)
+#define DL_FLAG_AUTOREMOVE_S	BIT(4)
 
 /**
  * struct device_link - Device link representation.
-- 
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