[RFC PATCH net-next 1/5] net: dsa: realtek-smi: fix mdio_free bug on module unload

["Alvin Šipraga" <alvin@pqrs.dk>]

From: Alvin Šipraga <alsi@bang-olufsen.dk>

realtek-smi-core fails to unregister the slave MII bus on module unload,
raising the following BUG warning:

    mdio_bus.c:650: BUG_ON(bus->state != MDIOBUS_UNREGISTERED);

    kernel BUG at drivers/net/phy/mdio_bus.c:650!
    Internal error: Oops - BUG: 0 [#1] PREEMPT_RT SMP
    Call trace:
     mdiobus_free+0x4c/0x50
     devm_mdiobus_free+0x18/0x20
     release_nodes.isra.0+0x1c0/0x2b0
     devres_release_all+0x38/0x58
     device_release_driver_internal+0x124/0x1e8
     driver_detach+0x54/0xe0
     bus_remove_driver+0x60/0xd8
     driver_unregister+0x34/0x60
     platform_driver_unregister+0x18/0x20
     realtek_smi_driver_exit+0x14/0x1c [realtek_smi]

Fix this by duly unregistering the slave MII bus with
mdiobus_unregister. We do this in the DSA teardown path, since
registration is performed in the DSA setup path.

Cc: Linus Walleij <linus.walleij@linaro.org>
Fixes: d8652956cf37 ("net: dsa: realtek-smi: Add Realtek SMI driver")
Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
---
 drivers/net/dsa/realtek-smi-core.c | 6 ++++++
 drivers/net/dsa/realtek-smi-core.h | 1 +
 drivers/net/dsa/rtl8366rb.c        | 8 ++++++++
 3 files changed, 15 insertions(+)

diff --git a/drivers/net/dsa/realtek-smi-core.c b/drivers/net/dsa/realtek-smi-core.c
index 8e49d4f85d48..6992b6b31db6 100644
--- a/drivers/net/dsa/realtek-smi-core.c
+++ b/drivers/net/dsa/realtek-smi-core.c
@@ -383,6 +383,12 @@ int realtek_smi_setup_mdio(struct realtek_smi *smi)
 	return ret;
 }
 
+void realtek_smi_teardown_mdio(struct realtek_smi *smi)
+{
+	if (smi->slave_mii_bus)
+		mdiobus_unregister(smi->slave_mii_bus);
+}
+
 static int realtek_smi_probe(struct platform_device *pdev)
 {
 	const struct realtek_smi_variant *var;
diff --git a/drivers/net/dsa/realtek-smi-core.h b/drivers/net/dsa/realtek-smi-core.h
index fcf465f7f922..6cfa5f2df7ea 100644
--- a/drivers/net/dsa/realtek-smi-core.h
+++ b/drivers/net/dsa/realtek-smi-core.h
@@ -119,6 +119,7 @@ struct realtek_smi_variant {
 int realtek_smi_write_reg_noack(struct realtek_smi *smi, u32 addr,
 				u32 data);
 int realtek_smi_setup_mdio(struct realtek_smi *smi);
+void realtek_smi_teardown_mdio(struct realtek_smi *smi);
 
 /* RTL8366 library helpers */
 int rtl8366_mc_is_used(struct realtek_smi *smi, int mc_index, int *used);
diff --git a/drivers/net/dsa/rtl8366rb.c b/drivers/net/dsa/rtl8366rb.c
index a89093bc6c6a..6537fac7aba4 100644
--- a/drivers/net/dsa/rtl8366rb.c
+++ b/drivers/net/dsa/rtl8366rb.c
@@ -982,6 +982,13 @@ static int rtl8366rb_setup(struct dsa_switch *ds)
 	return 0;
 }
 
+static void rtl8366rb_teardown(struct dsa_switch *ds)
+{
+	struct realtek_smi *smi = ds->priv;
+
+	realtek_smi_teardown_mdio(smi);
+}
+
 static enum dsa_tag_protocol rtl8366_get_tag_protocol(struct dsa_switch *ds,
 						      int port,
 						      enum dsa_tag_protocol mp)
@@ -1505,6 +1512,7 @@ static int rtl8366rb_detect(struct realtek_smi *smi)
 static const struct dsa_switch_ops rtl8366rb_switch_ops = {
 	.get_tag_protocol = rtl8366_get_tag_protocol,
 	.setup = rtl8366rb_setup,
+	.teardown = rtl8366rb_teardown,
 	.phylink_mac_link_up = rtl8366rb_mac_link_up,
 	.phylink_mac_link_down = rtl8366rb_mac_link_down,
 	.get_strings = rtl8366_get_strings,
-- 
2.32.0