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

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Message-ID: <1421686560.4459.400.camel@spandruv-desktop.jf.intel.com>
Date:	Mon, 19 Jan 2015 16:56:45 +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

On Mon, 2015-01-19 at 18:49 +0200, Daniel Baluta wrote: 
> On Mon, Jan 19, 2015 at 6:44 PM, Pandruvada, Srinivas
> <srinivas.pandruvada@...el.com> wrote:
> > On Mon, 2015-01-19 at 16:40 +0200, Daniel Baluta wrote:
> >> Hello,
> >>
> >> On Sat, Dec 20, 2014 at 11:29 PM, Pandruvada, Srinivas
> >> <srinivas.pandruvada@...el.com> wrote:
> >> > +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.
> >>
> >> You are right about this. Under normal circumstances, if probe is called
> >> then acpi_match_device will not fail. I even tried to remove the
> >> device after probe
> >> but before acpi_match_device, anyhow acpi_match_device was still successful :)
> >>
> >> This is more a matter of code correctness.
> >>
> >> In ak8975_match_acpi_device we have:
> >>
> >> »       const struct acpi_device_id *id;
> >>
> >> »       id = acpi_match_device(dev->driver->acpi_match_table, dev);
> >> »       if (!id)
> >> »       »       return NULL;
> >> »       *chipset = (int)id->driver_data;
> >>
> >> Compiler complains on the fact that chipset might be uninitialized
> >> if this returns NULL, and we shouldn't ignore this warning even this case
> >> will never happen.
> >>
> > Will this fix?
> > data->chipset = AK8975;
> > before
> > ak8975_match_acpi_device(&client->dev, &data->chipset);
> >
> 
> Yes, this is done in the original patch:
> 
> +       *chipset = AK_MAX_TYPE;
Since data memory is not zero alloced, other member of data are anyway
initialized, so adding this also may be better. 
> 
> .. and fixes the warning.
> 
> Daniel.