[PATCH v1] driver core: Update device link status correctly for SYNC_STATE_ONLY links

[Saravana Kannan]

When SYNC_STATE_ONLY support was added in commit 05ef983e0d65 ("driver
core: Add device link support for SYNC_STATE_ONLY flag"),
SYNC_STATE_ONLY links were treated similar to STATELESS links in terms
of not blocking consumer probe if the supplier hasn't probed yet.

That caused a SYNC_STATE_ONLY device link's status to not get updated.
Since SYNC_STATE_ONLY device link is no longer useful once the
consumer probes, commit 21c27f06587d ("driver core: Fix
SYNC_STATE_ONLY device link implementation") addresses the status
update issue by deleting the SYNC_STATE_ONLY device link instead of
complicating the status update code.

However, there are still some cases where we need to update the status
of a SYNC_STATE_ONLY device link.  A SYNC_STATE_ONLY device link can
later get converted into a normal MANAGED device link when a normal
MANAGED device link is created between a supplier and consumer that
already have a SYNC_STATE_ONLY device link between them. If a
SYNC_STATE_ONLY device link's status isn't maintained correctly till
it's converted to a normal MANAGED device link, then the normal
MANAGED device link will end up with a wrong link status. This can
cause a warning stack trace[1] when the consumer device probes.

This commit fixes the SYNC_STATE_ONLY device link status update issue
where it wouldn't transition correctly from DL_STATE_AVAILABLE to
DL_STATE_CONSUMER_PROBE.

[1] - https://lore.kernel.org/lkml/20200522204120.3b3c9ed6@apollo/
Fixes: 05ef983e0d65 ("driver core: Add device link support for SYNC_STATE_ONLY flag")
Fixes: 21c27f06587d ("driver core: Fix SYNC_STATE_ONLY device link implementation")
Reported-by: Michael Walle <michael@xxxxxxxx>
Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>
---
Greg,

I think this is the issue Michael ran into. I'd like him to test the fix
before it's pulled in.

Michael,

If you can test this on the branch you saw the issue in and give a
Tested-by if it works, that'd be great.

Thanks,
Saravana

 drivers/base/core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 791b7530599f..9511be3f9a32 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -687,11 +687,11 @@ int device_links_check_suppliers(struct device *dev)
 	device_links_write_lock();
 
 	list_for_each_entry(link, &dev->links.suppliers, c_node) {
-		if (!(link->flags & DL_FLAG_MANAGED) ||
-		    link->flags & DL_FLAG_SYNC_STATE_ONLY)
+		if (!(link->flags & DL_FLAG_MANAGED))
 			continue;
 
-		if (link->status != DL_STATE_AVAILABLE) {
+		if (link->status != DL_STATE_AVAILABLE &&
+		    !(link->flags & DL_FLAG_SYNC_STATE_ONLY)) {
 			device_links_missing_supplier(dev);
 			ret = -EPROBE_DEFER;
 			break;
-- 
2.27.0.rc0.183.gde8f92d652-goog