[PATCH net-next] net: dsa: mt7530: register OF node for internal MDIO bus

[Arınç ÜNAL]

On 21.12.2023 18:16, Vladimir Oltean wrote:
> On Wed, Dec 20, 2023 at 07:35:39PM +0200, Arınç ÜNAL wrote:
>> From: David Bauer <mail at david-bauer.net>
>>
>> The MT753x switches provide a switch-internal MDIO bus for the embedded
>> PHYs.
>>
>> Register a OF sub-node on the switch OF-node for this internal MDIO bus.
>> This allows to configure the embedded PHYs using device-tree.
>>
>> Signed-off-by: David Bauer <mail at david-bauer.net>
>> Signed-off-by: Daniel Golle <daniel at makrotopia.org>
>> Signed-off-by: Arınç ÜNAL <arinc.unal at arinc9.com>
>> ---
> 
> Can you please not assign "bus" to ds->user_mii_bus unless there is no
> "mdio" OF node? We don't need ds->user_mii_bus populated when it is
> described in device tree.

Do you mean like this:

diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
index 391c4dbdff42..d239462a4bd8 100644
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -2155,15 +2155,21 @@ mt7530_setup_mdio(struct mt7530_priv *priv)
  {
  	struct dsa_switch *ds = priv->ds;
  	struct device *dev = priv->dev;
+	struct device_node *np, *mnp;
  	struct mii_bus *bus;
  	static int idx;
  	int ret;
  
+	np = priv->dev->of_node;
+	mnp = of_get_child_by_name(np, "mdio");
+
  	bus = devm_mdiobus_alloc(dev);
  	if (!bus)
  		return -ENOMEM;
  
-	ds->user_mii_bus = bus;
+	if (mnp == NULL)
+		ds->user_mii_bus = bus;
+
  	bus->priv = priv;
  	bus->name = KBUILD_MODNAME "-mii";
  	snprintf(bus->id, MII_BUS_ID_SIZE, KBUILD_MODNAME "-%d", idx++);
@@ -2177,7 +2183,8 @@ mt7530_setup_mdio(struct mt7530_priv *priv)
  	if (priv->irq)
  		mt7530_setup_mdio_irq(priv);
  
-	ret = devm_mdiobus_register(dev, bus);
+	ret = devm_of_mdiobus_register(dev, bus, mnp);
+	of_node_put(mnp);
  	if (ret) {
  		dev_err(dev, "failed to register MDIO bus: %d\n", ret);
  		if (priv->irq)

If the MDIO bus of the switch is defined on the devicetree, the
(!ds->user_mii_bus && ds->ops->phy_read) check in dsa_switch_setup will be
true so the MDIO bus will be attempted to be registered again, resulting in
a kernel panic.

[    1.369012] mt7530-mdio mdio-bus:1f: MT7530 adapts as multi-chip module
[    1.391552] CPU 0 Unable to handle kernel paging request at virtual address 00000700, epc == 802eb948, ra == 802eb938
[    1.402205] Oops[#1]:
[    1.404481] CPU: 0 PID: 26 Comm: kworker/u5:1 Not tainted 6.7.0-rc6-next-20231222-00012-g9997041f4e67-dirty #281
[    1.414622] Hardware name: UniElec U7621-06 (16M flash)
[    1.419829] Workqueue: events_unbound deferred_probe_work_func
[    1.425664] $ 0   : 00000000 00000001 00000011 00000700
[    1.430895] $ 4   : 00000700 814d0000 00000000 00000000
[    1.436123] $ 8   : 00000001 00000011 00000011 81595a80
[    1.441353] $12   : 81595a80 81595ad8 81595a80 81595ad8
[    1.446585] $16   : 81589a80 00000000 82019000 81589600
[    1.451815] $20   : 807d4a88 8205a280 00000005 00000000
[    1.457045] $24   : 00000000 802efd60
[    1.462274] $28   : 81594000 81595c18 80760000 802eb938
[    1.467505] Hi    : 00000000
[    1.470371] Lo    : 00000000
[    1.473235] epc   : 802eb948 mt753x_setup+0x39c/0x3bc
[    1.478283] ra    : 802eb938 mt753x_setup+0x38c/0x3bc
[    1.483324] Status: 11000403	KERNEL EXL IE
[    1.487508] Cause : 4080000c (ExcCode 03)
[    1.491502] BadVA : 00000700
[    1.494367] PrId  : 0001992f (MIPS 1004Kc)
[    1.498446] Process kworker/u5:1 (pid: 26, threadinfo=(ptrval), task=(ptrval), tls=00000000)
[    1.506853] Stack : 7fffffff 00000000 8205a280 00000000 806a8ab8 81589a80 8205a280 81521f00
[    1.515224]         81521f08 8157dc00 806ba49c 8205a280 00000001 804c6374 81589e00 81589c80
[    1.523601]         806a5ed0 81589600 00000000 81595c9c 805cab30 806d0000 8069e96c 806b99cc
[    1.531971]         00000006 00000dc0 ffffffff 802bd188 81589600 802bd29c fffffff4 fffffff4
[    1.540341]         8205a480 807d339c 00000000 00000000 00000000 00000000 00000000 00000000
[    1.548707]         ...
[    1.551150] Call Trace:
[    1.553583] [<802eb948>] mt753x_setup+0x39c/0x3bc
[    1.558286] [<804c6374>] dsa_register_switch+0x924/0xcc4
[    1.563592] [<802ddad0>] mdio_probe+0x34/0x6c
[    1.567943] [<802b95d0>] really_probe+0x16c/0x2dc
[    1.572639] [<802b995c>] driver_probe_device+0x40/0xd0
[    1.577767] [<802b9a4c>] __device_attach_driver+0x60/0xe8
[    1.583154] [<802b7694>] bus_for_each_drv+0xc8/0xf4
[    1.588042] [<802b9d8c>] __device_attach+0xd8/0x14c
[    1.592912] [<802b831c>] bus_probe_device+0x48/0xd8
[    1.597788] [<802b8f5c>] deferred_probe_work_func+0xb4/0xcc
[    1.603348] [<8003ab1c>] process_scheduled_works+0x1dc/0x2b8
[    1.609015] [<8003b1b0>] worker_thread+0x2dc/0x330
[    1.613804] [<80041d4c>] kthread+0xf8/0x100
[    1.617996] [<80002a18>] ret_from_kernel_thread+0x14/0x1c
[    1.623385]
[    1.624869] Code: 8ea30030  00042080  00641821 <ac620000> 26310001  1636fff1  00003825  1000ff67  02803025
[    1.634638]
[    1.636435] ---[ end trace 0000000000000000 ]---

Arınç