linux-kernel - Re: [RFC PATCH] iio: ak8975: Make sure chipset is always initialized

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Message-ID: <1419110952.2843.8.camel@spandruv-hsb-test>
Date:	Sat, 20 Dec 2014 21:29:12 +0000
From:	"Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>
To:	"Baluta, Daniel" <daniel.baluta@...el.com>
CC:	"lars@...afoo.de" <lars@...afoo.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"knaack.h@....de" <knaack.h@....de>,
	"jic23@...nel.org" <jic23@...nel.org>,
	"Purdila, Octavian" <octavian.purdila@...el.com>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"Westerberg, Mika" <mika.westerberg@...el.com>,
	"pmeerw@...erw.net" <pmeerw@...erw.net>,
	"beomho.seo@...sung.com" <beomho.seo@...sung.com>,
	"gwendal@...omium.org" <gwendal@...omium.org>
Subject: Re: [RFC PATCH] iio: ak8975: Make sure chipset is always initialized

+Mika

On Sat, 2014-12-20 at 13:26 -0800, Srinivas Pandruvada wrote:
> On Sat, 2014-12-20 at 00:25 +0200, Daniel Baluta wrote:
> > On Sat, Dec 20, 2014 at 12:16 AM, Hartmut Knaack <knaack.h@....de> wrote:
> > > Daniel Baluta schrieb am 18.12.2014 um 18:16:
> > >> When using ACPI, if acpi_match_device fails then chipset enum will be
> > >> uninitialized and &ak_def_array[chipset] will point to some bad address.
> > >>
> I am missing something. You are enumerated over i2c device, which was
> created from ACPI PNP resource. There is a valid handle or and the
> device has an ACPI companion at the least. If this failing, I have to
> check the code for acpi i2c.
> Can you check why this check failed? We may have bug in i2c handling.
> 
> Thanks,
> Srinivas
> 
> > >> This fixes the following compilation warning:
> > >>
> > >> 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];
> > >>
> > >> Reported-by: Octavian Purdila <octavian.purdila@...el.com>
> > >> Signed-off-by: Daniel Baluta <daniel.baluta@...el.com>
> > >> ---
> > >> This is a RFC because while I'm pretty sure that chipset should be initialized
> > >> with AK_MAX_TYPE in ak8975_match_acpi_device, I am not sure if we can live with
> > >> a NULL return value of ak8975_match_acpi_device. Current implementation ignores
> > >> return value of ak8975_match_acpi_device.
> > > This seems to be the actual problem: these _match_acpi_device functions return
> > > NULL on failure, and this should be checked for.
> > 
> > Ok, so this would acceptable?
> > 
> > diff --git a/drivers/iio/magnetometer/ak8975.c
> > b/drivers/iio/magnetometer/ak8975.c
> > index 0d10a4b..68d99e9 100644
> > --- a/drivers/iio/magnetometer/ak8975.c
> > +++ b/drivers/iio/magnetometer/ak8975.c
> > @@ -776,8 +776,9 @@ static int ak8975_probe(struct i2c_client *client,
> >                 name = id->name;
> >         } else if (ACPI_HANDLE(&client->dev))
> >                 name = ak8975_match_acpi_device(&client->dev, &chipset);
> > -       else
> > -               return -ENOSYS;
> > +
> > +       if (!name)
> > +               return -ENODEV;
> > 
> > 
> > I still have some doubts about return code in case of error.
> > 
> > For ak8975 we use -ENOSYS, but for kxcjk-1013 we use -ENODEV.
> > 
> > I will send a patch after we clear this out.
> > 
> > thanks,
> > Daniel.
>