firmware: arm_ffa: Move the FF-A v1.0 NULL UUID workaround to bus notifier

Currently FF-A bus ffa_device_match() handles the workaround for the
FF-A v1.0 devices which are not populated with UUID to match. The FF-A
bus layer calls into FF-A driver and populates the device UUID if it
matches with the driver attempting to match.

But this forces to have both FF-A bus and core driver to be bundled into
a single module. However, keep it as a single module adds problems for
the FF-A driver registrations and their initcall levels.

In preparation to split the FF-A bus and the core driver into distinct
modules, we need to move the workaround away from the FF-A bus layer.
We can add it into the FF-A core driver as a bus notifier.

In order to do so, we need to always match any driver with the device if
the UUID is NULL and then during the driver binding phase, we can populate
the UUID if it matches with the driver UUID table using the bus notifiers.
We also need to add a check for NULL UUID before calling the device/driver
probe as devices with NULL UUID is possible since we match all for that
case.
Acked-by: Sebastian Ene <sebastianene@google.com>
Link: https://lore.kernel.org/r/20240515094028.1947976-1-sudeep.holla@arm.comSigned-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_ffa/bus.c

@@ -30,12 +30,11 @@ static int ffa_device_match(struct device *dev, struct device_driver *drv)
 	while (!uuid_is_null(&id_table->uuid)) {
 		/*
 		 * FF-A v1.0 doesn't provide discovery of UUIDs, just the
-		 * partition IDs, so fetch the partitions IDs for this
-		 * id_table UUID and assign the UUID to the device if the
-		 * partition ID matches
+		 * partition IDs, so match it unconditionally here and handle
+		 * it via the installed bus notifier during driver binding.
 		 */
 		if (uuid_is_null(&ffa_dev->uuid))
-			ffa_device_match_uuid(ffa_dev, &id_table->uuid);
+			return 1;
 
 		if (uuid_equal(&ffa_dev->uuid, &id_table->uuid))
 			return 1;
@@ -50,6 +49,10 @@ static int ffa_device_probe(struct device *dev)
 	struct ffa_driver *ffa_drv = to_ffa_driver(dev->driver);
 	struct ffa_device *ffa_dev = to_ffa_dev(dev);
 
+	/* UUID can be still NULL with FF-A v1.0, so just skip probing them */
+	if (uuid_is_null(&ffa_dev->uuid))
+		return -ENODEV;
+
 	return ffa_drv->probe(ffa_dev);
 }
 

drivers/firmware/arm_ffa/driver.c

@@ -1224,14 +1224,6 @@ void ffa_device_match_uuid(struct ffa_device *ffa_dev, const uuid_t *uuid)
 	int count, idx;
 	struct ffa_partition_info *pbuf, *tpbuf;
 
-	/*
-	 * FF-A v1.1 provides UUID for each partition as part of the discovery
-	 * API, the discovered UUID must be populated in the device's UUID and
-	 * there is no need to copy the same from the driver table.
-	 */
-	if (drv_info->version > FFA_VERSION_1_0)
-		return;
-
 	count = ffa_partition_probe(uuid, &pbuf);
 	if (count <= 0)
 		return;
@@ -1242,6 +1234,35 @@ void ffa_device_match_uuid(struct ffa_device *ffa_dev, const uuid_t *uuid)
 	kfree(pbuf);
 }
 
+static int
+ffa_bus_notifier(struct notifier_block *nb, unsigned long action, void *data)
+{
+	struct device *dev = data;
+	struct ffa_device *fdev = to_ffa_dev(dev);
+
+	if (action == BUS_NOTIFY_BIND_DRIVER) {
+		struct ffa_driver *ffa_drv = to_ffa_driver(dev->driver);
+		const struct ffa_device_id *id_table= ffa_drv->id_table;
+
+		/*
+		 * FF-A v1.1 provides UUID for each partition as part of the
+		 * discovery API, the discovered UUID must be populated in the
+		 * device's UUID and there is no need to workaround by copying
+		 * the same from the driver table.
+		 */
+		if (uuid_is_null(&fdev->uuid))
+			ffa_device_match_uuid(fdev, &id_table->uuid);
+
+		return NOTIFY_OK;
+	}
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block ffa_bus_nb = {
+	.notifier_call = ffa_bus_notifier,
+};
+
 static int ffa_setup_partitions(void)
 {
 	int count, idx, ret;
@@ -1250,6 +1271,12 @@ static int ffa_setup_partitions(void)
 	struct ffa_dev_part_info *info;
 	struct ffa_partition_info *pbuf, *tpbuf;
 
+	if (drv_info->version == FFA_VERSION_1_0) {
+		ret = bus_register_notifier(&ffa_bus_type, &ffa_bus_nb);
+		if (ret)
+			pr_err("Failed to register FF-A bus notifiers\n");
+	}
+
 	count = ffa_partition_probe(&uuid_null, &pbuf);
 	if (count <= 0) {
 		pr_info("%s: No partitions found, error %d\n", __func__, count);
@@ -1261,7 +1288,7 @@ static int ffa_setup_partitions(void)
 		import_uuid(&uuid, (u8 *)tpbuf->uuid);
 
 		/* Note that if the UUID will be uuid_null, that will require
-		 * ffa_device_match() to find the UUID of this partition id
+		 * ffa_bus_notifier() to find the UUID of this partition id
 		 * with help of ffa_device_match_uuid(). FF-A v1.1 and above
 		 * provides UUID here for each partition as part of the
 		 * discovery API and the same is passed.