Re: [PATCH] net: dsa: mv88e6xxx: add warning for truncated mdio bus id

[Florian Fainelli]

On 3/20/2024 7:33 AM, Josua Mayer wrote:
> Am 20.03.24 um 15:09 schrieb Jiri Pirko:
> > Wed, Mar 20, 2024 at 02:48:55PM CET, josua@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx>
> > 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.
> Correct, thanks - will do.
> Just for future reference for those occasional contributors -
> is there such a thing as an lkml calendar?

There is this: https://patchwork.hopto.org/net-next.html

> > > ---
> > > 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?
> Duplicate could be avoided by truncating from the start,
> however I don't know if that is a good idea.
> It affects naming of paths in sysfs, and the root cause is
> difficult to spot.
> > > 	} 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?
> It can happen on switch nodes at deep levels in the device-tree,
> while describing both internal and external mdio buses of a switch.
> E.g. Documentation/devicetree/bindings/net/dsa/marvell,mv88e6xxx.yaml

We should consider moving these types of checks into the MDIO bus core, 
or at least introduce a helper function such that it embeds the check in it.
--
Florian