bus: fsl-mc: do not add a device-link for the UAPI used DPMCP device

BugLink: https://bugs.launchpad.net/bugs/2120812

commit dd7d8e012b23de158ca0188239c7a1f2a83b4484 upstream.

The fsl-mc bus associated to the root DPRC in a DPAA2 system exports a
device file for userspace access to the MC firmware. In case the DPRC's
local MC portal (DPMCP) is currently in use, a new DPMCP device is
allocated through the fsl_mc_portal_allocate() function.

In this case, the call to fsl_mc_portal_allocate() will fail with -EINVAL
when trying to add a device link between the root DPRC (consumer) and
the newly allocated DPMCP device (supplier). This is because the DPMCP
is a dependent of the DPRC device (the bus).

Fix this by not adding a device link in case the DPMCP is allocated for
the root DPRC's usage.

Fixes: afb7742 ("bus: fsl-mc: automatically add a device_link on fsl_mc_[portal,object]_allocate")
Signed-off-by: Ioana Ciornei <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christophe Leroy <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Noah Wager <[email protected]>
Signed-off-by: Stefan Bader <[email protected]>

Author: IoanaCiornei

drivers/bus/fsl-mc/mc-io.c

@@ -214,12 +214,19 @@ int __must_check fsl_mc_portal_allocate(struct fsl_mc_device *mc_dev,
 	if (error < 0)
 		goto error_cleanup_resource;
 
-	dpmcp_dev->consumer_link = device_link_add(&mc_dev->dev,
-						   &dpmcp_dev->dev,
-						   DL_FLAG_AUTOREMOVE_CONSUMER);
-	if (!dpmcp_dev->consumer_link) {
-		error = -EINVAL;
-		goto error_cleanup_mc_io;
+	/* If the DPRC device itself tries to allocate a portal (usually for
+	 * UAPI interaction), don't add a device link between them since the
+	 * DPMCP device is an actual child device of the DPRC and a reverse
+	 * dependency is not allowed.
+	 */
+	if (mc_dev != mc_bus_dev) {
+		dpmcp_dev->consumer_link = device_link_add(&mc_dev->dev,
+							   &dpmcp_dev->dev,
+							   DL_FLAG_AUTOREMOVE_CONSUMER);
+		if (!dpmcp_dev->consumer_link) {
+			error = -EINVAL;
+			goto error_cleanup_mc_io;
+		}
 	}
 
 	*new_mc_io = mc_io;