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

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Message-ID: <CAEnQRZDwSH7kKygih6Mu32rUdEJ_OA0M0FfOWtUmf8iL7p6+3Q@mail.gmail.com>
Date:	Sat, 20 Dec 2014 23:40:18 +0200
From:	Daniel Baluta <daniel.baluta@...el.com>
To:	"Pandruvada, Srinivas" <srinivas.pandruvada@...el.com>
Cc:	"Baluta, Daniel" <daniel.baluta@...el.com>,
	"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

I will have closer look on why acpi_match_device could fail. This patch
was only based on code reading when trying to fix the compiler warning
mentioned in the commit message.

[Sorry for top posting]

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.
>>
>> 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.
>>
>
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