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

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Date:	Sat, 20 Dec 2014 13:26:36 -0800
From:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:	Daniel Baluta <daniel.baluta@...el.com>
Cc:	Hartmut Knaack <knaack.h@....de>,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>, gwendal@...omium.org,
	beomho.seo@...sung.com,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"octavian.purdila@...el.com" <octavian.purdila@...el.com>
Subject: Re: [RFC PATCH] iio: ak8975: Make sure chipset is always initialized

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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