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Date: Wed, 20 Mar 2024 15:09:01 +0100
From: Jiri Pirko <jiri@resnulli.us>
To: Josua Mayer <josua@solid-run.com>
Cc: Andrew Lunn <andrew@lunn.ch>, Florian Fainelli <f.fainelli@gmail.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net: dsa: mv88e6xxx: add warning for truncated mdio bus
 id
Message-ID: <Zfrt_dlYvBzlxull@nanopsycho>
References: <20240320-mv88e6xxx-truncate-busid-v1-1-cface50b2efb@solid-run.com>
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In-Reply-To: <20240320-mv88e6xxx-truncate-busid-v1-1-cface50b2efb@solid-run.com>

Wed, Mar 20, 2024 at 02:48:55PM CET, josua@solid-run.com wrote:
>mv88e6xxx supports multiple mdio buses as children, e.g. to model both
>internal and external phys. If the child buses mdio ids are truncated,
>they might collide which each other leading to an obscure error from
>kobject_add.
>
>The maximum length of bus id is currently defined as 61
>(MII_BUS_ID_SIZE). Truncation can occur on platforms with long node
>names and multiple levels before the parent bus on whiich the dsa switch

s/whiich/which/


>sits such as on CN9130 [1].
>
>Test whether the return value of snprintf exceeds the maximum bus id
>length and print a warning.
>
>[1]
>[    8.324631] mv88e6085 f212a200.mdio-mii:04: switch 0x1760 detected: Marvell 88E6176, revision 1
>[    8.389516] mv88e6085 f212a200.mdio-mii:04: Truncated bus-id may collide.
>[    8.592367] mv88e6085 f212a200.mdio-mii:04: Truncated bus-id may collide.
>[    8.623593] sysfs: cannot create duplicate filename '/devices/platform/cp0/cp0:config-space@f2000000/f212a200.mdio/mdio_bus/f212a200.mdio-mii/f212a200.mdio-mii:04/mdio_bus/!cp0!config-space@f2000000!mdio@12a200!ethernet-switch@4!mdi'
>[    8.785480] kobject: kobject_add_internal failed for !cp0!config-space@f2000000!mdio@12a200!ethernet-switch@4!mdi with -EEXIST, don't try to register things with the same name in the same directory.
>[    8.936514] libphy: mii_bus /cp0/config-space@f2000000/mdio@12a200/ethernet-switch@4/mdi failed to register
>[    8.946300] mdio_bus !cp0!config-space@f2000000!mdio@12a200!ethernet-switch@4!mdi: __mdiobus_register: -22
>[    8.956003] mv88e6085 f212a200.mdio-mii:04: Cannot register MDIO bus (-22)
>[    8.965329] mv88e6085: probe of f212a200.mdio-mii:04 failed with error -22
>
>Signed-off-by: Josua Mayer <josua@solid-run.com>

This is not bug fix, assume you target net-next. Please:
1) Next time, indicate that in the patch subject like this:
   [patch net-next] xxx
2) net-next is currently closed, repost next week.


>---
> drivers/net/dsa/mv88e6xxx/chip.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
>index 614cabb5c1b0..1c40f7631ab1 100644
>--- a/drivers/net/dsa/mv88e6xxx/chip.c
>+++ b/drivers/net/dsa/mv88e6xxx/chip.c
>@@ -3731,10 +3731,12 @@ static int mv88e6xxx_mdio_register(struct mv88e6xxx_chip *chip,
> 
> 	if (np) {
> 		bus->name = np->full_name;
>-		snprintf(bus->id, MII_BUS_ID_SIZE, "%pOF", np);
>+		if (snprintf(bus->id, MII_BUS_ID_SIZE, "%pOF", np) >= MII_BUS_ID_SIZE)
>+			dev_warn(chip->dev, "Truncated bus-id may collide.\n");

How about instead of warn&fail fallback to some different name in this
case?


> 	} else {
> 		bus->name = "mv88e6xxx SMI";
>-		snprintf(bus->id, MII_BUS_ID_SIZE, "mv88e6xxx-%d", index++);
>+		if (snprintf(bus->id, MII_BUS_ID_SIZE, "mv88e6xxx-%d", index++) >= MII_BUS_ID_SIZE)

How exactly this may happen?


>+			dev_warn(chip->dev, "Truncated bus-id may collide.\n");
> 	}
> 
> 	bus->read = mv88e6xxx_mdio_read;
>
>---
>base-commit: e8f897f4afef0031fe618a8e94127a0934896aba
>change-id: 20240320-mv88e6xxx-truncate-busid-34a1d2769bbf
>
>Sincerely,
>-- 
>Josua Mayer <josua@solid-run.com>
>
>