Re: [PATCH] net: dsa: mv88e6xxx: initialize return variable on declaration

Marek Behún
2021-12-06T22:30:24Z

On Mon, 6 Dec 2021 14:21:03 +0100
Andrew Lunn <andrew@lunn.ch> wrote:

> On Mon, Dec 06, 2021 at 04:32:19PM +0500, Ameer Hamza wrote:
> > Uninitialized err variable defined in mv88e6393x_serdes_power
> > function may cause undefined behaviour if it is called from
> > mv88e6xxx_serdes_power_down context.
> >
> > Addresses-Coverity: 1494644 ("Uninitialized scalar variable")
> >
> > Signed-off-by: Ameer Hamza <amhamza.mgc@gmail.com>
> > ---
> > drivers/net/dsa/mv88e6xxx/serdes.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/dsa/mv88e6xxx/serdes.c b/drivers/net/dsa/mv88e6xxx/serdes.c
> > index 55273013bfb5..33727439724a 100644
> > --- a/drivers/net/dsa/mv88e6xxx/serdes.c
> > +++ b/drivers/net/dsa/mv88e6xxx/serdes.c
> > @@ -1507,7 +1507,7 @@ int mv88e6393x_serdes_power(struct mv88e6xxx_chip *chip, int port, int lane,
> > bool on)
> > {
> > u8 cmode = chip->ports[port].cmode;
> > - int err;
> > + int err = 0;
> >
> > if (port != 0 && port != 9 && port != 10)
> > return -EOPNOTSUPP;
>
> Hi Marek
>
> This warning likely comes from cmode not being a SERDES mode, and that
> is not handles in the switch statementing. Do we want an
>
> default:
> err = EINVAL;
>
> ?
>
> Andrew

Hi Andrew,

currently all the .serdes_power() methods return 0 for non-serdes ports.
This is because the way it is written, these methods are not called if
there is not a serdes lane for a given port.

For this issue with err variable undefined, to fix it we should simply
set int err=0 at the beginning of mv88e6393x_serdes_power(), to make it
behave like other serdes_power() methods do in serdes.c.

But a refactor may be needed for serdes_power() methods, at least
because they are a little weird. But it should be unrelated to this fix.

In serdes.h we have static inline functions
mv88e6xxx_serdes_power_up(chip, port, lane)
mv88e6xxx_serdes_power_down(chip, port, lane)

(These simply call the serdes_power() method of chip ops, with
additional boolean argument to specify powerup/powerdown.
Also for these we first need to determine lane for a port. If lane
does not exists, these should not be called.)

In chip.c we have function
mv88e6xxx_serdes_power(chip, port, on)

(This finds if the port has a lane, and if so, calls, if on=true
mv88e6xxx_serdes_power_up()
from serdes.h, and then
mv88e6xxx_serdes_irq_request()
also from serdes.h

and if on=false, calls _irq_free() & _serdes_power_down()
)

So if I call
mv88e6xxx_serdes_power(chip, port, true)
it goes
mv88e6xxx_serdes_power_up(chip, port, lane)
chip->info->ops->serdes_power(chip, port, lane, true)
so the `on` argument is used in some places, but in other places there
are two functions instead.

Which I find a little weird.

Marek