netdev - [PATCH 2/2] net: dsa: mv88e6xxx: fix marvell 6350 probe crash

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Date: Wed, 22 Nov 2023 23:21:16 +1000
From: Greg Ungerer <gerg@...nel.org>
To: rmk+kernel@...linux.org.uk,
	andrew@...n.ch,
	hkallweit1@...il.com
Cc: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	netdev@...r.kernel.org,
	Greg Ungerer <gerg@...nel.org>,
	Russell King <linux@...linux.org.uk>
Subject: [PATCH 2/2] net: dsa: mv88e6xxx: fix marvell 6350 probe crash

As of commit b92143d4420f ("net: dsa: mv88e6xxx: add infrastructure for
phylink_pcs") probing of a Marvell 88e6350 switch causes a NULL pointer
dereference like this example:

    ...
    mv88e6085 d0072004.mdio-mii:11: switch 0x3710 detected: Marvell 88E6350, revision 2
    8<--- cut here ---
    Unable to handle kernel NULL pointer dereference at virtual address 00000000 when read
    [00000000] *pgd=00000000
    Internal error: Oops: 5 [#1] ARM
    Modules linked in:
    CPU: 0 PID: 8 Comm: kworker/u2:0 Not tainted 6.7.0-rc2-dirty #26
    Hardware name: Marvell Armada 370/XP (Device Tree)
    Workqueue: events_unbound deferred_probe_work_func
    PC is at mv88e6xxx_port_setup+0x1c/0x44
    LR is at dsa_port_devlink_setup+0x74/0x154
    pc : [<c057ea24>]    lr : [<c0819598>]    psr: a0000013
    sp : c184fce0  ip : c542b8f4  fp : 00000000
    r10: 00000001  r9 : c542a540  r8 : c542bc00
    r7 : c542b838  r6 : c5244580  r5 : 00000005  r4 : c5244580
    r3 : 00000000  r2 : c542b840  r1 : 00000005  r0 : c1a02040
    ...

The Marvell 88e6350 switch has no SERDES interface and so has no
corresponding pcs_ops defined for it. But during probing a call is made
to mv88e6xxx_port_setup() which unconditionally expects pcs_ops to exist,
though the presence of the pcs_ops->pcs_init function is optional.

Modify the code to check for pcs_ops first, before checking for and calling
pcs_ops->pcs_init.

Fixes: b92143d4420f ("net: dsa: mv88e6xxx: add infrastructure for phylink_pcs")
Suggested-by: Russell King (Oracle) <linux@...linux.org.uk>
Signed-off-by: Greg Ungerer <gerg@...nel.org>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index e9adf9711c09..38f76ee3035b 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -3892,7 +3892,8 @@ static int mv88e6xxx_port_setup(struct dsa_switch *ds, int port)
 	struct mv88e6xxx_chip *chip = ds->priv;
 	int err;
 
-	if (chip->info->ops->pcs_ops->pcs_init) {
+	if (chip->info->ops->pcs_ops &&
+	    chip->info->ops->pcs_ops->pcs_init) {
 		err = chip->info->ops->pcs_ops->pcs_init(chip, port);
 		if (err)
 			return err;
-- 
2.25.1