linux-kernel - Re: [PATCH v4.4-rc8] iio: magnetometer: ak8975: Silence 'may be used uninitialized' warning

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Message-ID: <1452356229.4044.4.camel@linux.intel.com>
Date:	Sat, 09 Jan 2016 08:17:09 -0800
From:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:	Jonathan Cameron <jic23@...nel.org>, tim.gardner@...onical.com,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>
Subject: Re: [PATCH v4.4-rc8] iio: magnetometer: ak8975: Silence 'may be
 used uninitialized' warning

On Sat, 2016-01-09 at 16:00 +0000, Jonathan Cameron wrote:
> On 09/01/16 00:17, tim.gardner@...onical.com wrote:
> > From: Tim Gardner <tim.gardner@...onical.com>
> > 
> > drivers/iio/magnetometer/ak8975.c: In function 'ak8975_probe':
> > drivers/iio/magnetometer/ak8975.c:788:14: warning: 'chipset' may be
> > used uninitialized in this function [-Wmaybe-uninitialized]
> >   data->def = &ak_def_array[chipset];
> > 
> > gcc version 5.3.1 20151219 (Ubuntu 5.3.1-4ubuntu1)
> > 
> > Cc: Jonathan Cameron <jic23@...nel.org>
> > Cc: Hartmut Knaack <knaack.h@....de>
> > Cc: Lars-Peter Clausen <lars@...afoo.de>
> > Cc: Peter Meerwald <pmeerw@...erw.net>
> > Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> > Signed-off-by: Tim Gardner <tim.gardner@...onical.com>
> Doesn't look to be an actual bug as we either end up with chipset
> being filled
> based on the traditional match table in which case it'll be assigned
> or based on the acpi match, which should succeed seeing as we've
> already
> had to have matched one or the other for the probe to match in the
> first place.
> 
> So probably worth the change to make it easier to tell that it should
> be fine
> and suppress the warning.  However, whilst we are here, I note that
> *match_acpi_table has a path which returns NULL as the name and
> doesn't assign
> the chipset.  We should be therefore checking if (!name) return 
> -ENOSYS;
> Though maybe another error code would be more appropriate.
> 

Since in this case we are enumerated by ACPI using our match table, so
name can't be null. The "name" we provided in 
static const struct acpi_device_id ak_acpi_match[] = {..}
Same with the *chipset. Other than suppress warnings, I don't think it
will cause any real issue.

Thanks,
Srinivas 

> Not sure that error path can actually happen either, but if we are
> going to
> bother having the error path out of match_acpi_table then we ought to
> actually
> handle it!
> 
> Don't suppose you'd mind fixing that one as well whilst here?
> 
> Jonathan 
> > ---
> > 
> > This seems like a legitimate warning, though gcc should have
> > complained
> > about an earlier use of chipset on line 782.
> > 
> >  drivers/iio/magnetometer/ak8975.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/magnetometer/ak8975.c
> > b/drivers/iio/magnetometer/ak8975.c
> > index b13936d..80ec0ce 100644
> > --- a/drivers/iio/magnetometer/ak8975.c
> > +++ b/drivers/iio/magnetometer/ak8975.c
> > @@ -732,7 +732,7 @@ static int ak8975_probe(struct i2c_client
> > *client,
> >  	int eoc_gpio;
> >  	int err;
> >  	const char *name = NULL;
> > -	enum asahi_compass_chipset chipset;
> > +	enum asahi_compass_chipset chipset = AK_MAX_TYPE;
> >  
> >  	/* Grab and set up the supplied GPIO. */
> >  	if (client->dev.platform_data)
> > 
>