net: dsa: hellcreek: be compatible with masters which unregister on shutdown

Since commit 2f1e8ea7 ("net: dsa: link interfaces with the DSA
master to get rid of lockdep warnings"), DSA gained a requirement which
it did not fulfill, which is to unlink itself from the DSA master at
shutdown time.

Since the hellcreek driver was introduced after the bad commit, it has
never worked with DSA masters which decide to unregister their
net_device on shutdown, effectively hanging the reboot process.

Hellcreek is a platform device driver, so we probably cannot have the
oddities of ->shutdown and ->remove getting both called for the exact
same struct device. But to be in line with the pattern from the other
device drivers which are on slow buses, implement the same "if this then
not that" pattern of either running the ->shutdown or the ->remove hook.
The driver's current ->remove implementation makes that very easy
because it already zeroes out its device_drvdata on ->remove.

Fixes: e4b27ebc ("net: dsa: Add DSA driver for Hirschmann Hellcreek switches")
Link: https://lore.kernel.org/netdev/20210909095324.12978-1-LinoSanfilippo@gmx.de/Reported-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/hirschmann/hellcreek.c

@@ -1916,6 +1916,9 @@ static int hellcreek_remove(struct platform_device *pdev)
 {
 	struct hellcreek *hellcreek = platform_get_drvdata(pdev);
 
+	if (!hellcreek)
+		return 0;
+
 	hellcreek_hwtstamp_free(hellcreek);
 	hellcreek_ptp_free(hellcreek);
 	dsa_unregister_switch(hellcreek->ds);
@@ -1924,6 +1927,18 @@ static int hellcreek_remove(struct platform_device *pdev)
 	return 0;
 }
 
+static void hellcreek_shutdown(struct platform_device *pdev)
+{
+	struct hellcreek *hellcreek = platform_get_drvdata(pdev);
+
+	if (!hellcreek)
+		return;
+
+	dsa_switch_shutdown(hellcreek->ds);
+
+	platform_set_drvdata(pdev, NULL);
+}
+
 static const struct hellcreek_platform_data de1soc_r1_pdata = {
 	.name		 = "r4c30",
 	.num_ports	 = 4,
@@ -1946,6 +1961,7 @@ MODULE_DEVICE_TABLE(of, hellcreek_of_match);
 static struct platform_driver hellcreek_driver = {
 	.probe	= hellcreek_probe,
 	.remove = hellcreek_remove,
+	.shutdown = hellcreek_shutdown,
 	.driver = {
 		.name = "hellcreek",
 		.of_match_table = hellcreek_of_match,