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

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 6 Dec 2021 23:29:53 +0100 Marek Behún wrote:
> 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;
> > 
> > ?
> 
> 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.

Any objections to using a default case in the switch statement, tho?
I agree with Andrew that default statement would make the reasoning
clearer than just setting the variable at the start of the function.