linux-kernel - Re: [PATCH] iio: adc: meson-saradc: use NULL instead of 0 for pointer

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Date:   Tue, 6 Jun 2017 11:28:30 +0200
From:   Paolo Cretaro <paolocretaro@...il.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     Jonathan Cameron <jic23@...nel.org>, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: adc: meson-saradc: use NULL instead of 0 for pointer

Il 04/06/2017 15:32, Martin Blumenstingl ha scritto:
> Hi Paolo, Hi Jonathan,
> 
> On Sat, Jun 3, 2017 at 10:52 AM, Jonathan Cameron <jic23@...nel.org> wrote:
>> On Sun, 28 May 2017 23:17:57 +0200
>> Martin Blumenstingl <martin.blumenstingl@...glemail.com> wrote:
>>
>>> Hi Paolo, Hi Jonathan,
>>>
>>> On Sun, May 28, 2017 at 4:43 PM, Jonathan Cameron <jic23@...nel.org> wrote:
>>>> On Sun, 28 May 2017 13:24:38 +0200
>>>> Paolo Cretaro <paolocretaro@...il.com> wrote:
>>>>
>>>>> Fix sparse warning: Using plain integer as NULL pointer
>>>>>
>>>>> Signed-off-by: Paolo Cretaro <paolocretaro@...il.com>
>>>> This looks fine to me, but ideally you should always try to include
>>>> the driver author - particularly in the case of patches to a recent
>>>> driver such as this one.
>>>>
>>>> To that end I've cc'd Martin.
>>> thanks for spotting this (and providing a patch to fix it)
>>> this looks good to me, so:
>>> Acked-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
>>>
>>> if you can wait until next weekend then I can also test this on real hardware.
>> I've applied it to the togreg branch of iio.git but as that always goes out
>> as testing for at least a few days first (which I will happily rebase) give
>> me a shout if anything goes wrong!
> I have tested this on actual hardware and it seems that there's a bug
> in the meson-saradc driver (before and after this patch):
> if there are still "old" values in the FIFO then the driver currently
> crashes because regmap_read (regmap_mmio_read in case of the
> meson-saradc driver to be precise) de-references the "value" pointer
> (the parameter which we're trying to clean up here) -> this leads to a
> NULL de-reference. this happens regardless of whether we are passing
> "0" or "NULL"
> 
> I posted a patch which fixes the crash - and as a bonus this should
> also fix the sparse warning reported by Paolo:
> http://lists.infradead.org/pipermail/linux-amlogic/2017-June/003863.html
Nice, thanks!

Paolo
> 
>> Jonathan
>>>
>>>> Jonathan
>>>>> ---
>>>>>   drivers/iio/adc/meson_saradc.c | 2 +-
>>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/iio/adc/meson_saradc.c b/drivers/iio/adc/meson_saradc.c
>>>>> index 81cd39a57fe3..fb3f67a9ae1f 100644
>>>>> --- a/drivers/iio/adc/meson_saradc.c
>>>>> +++ b/drivers/iio/adc/meson_saradc.c
>>>>> @@ -481,7 +481,7 @@ static void meson_sar_adc_clear_fifo(struct iio_dev *indio_dev)
>>>>>                if (!meson_sar_adc_get_fifo_count(indio_dev))
>>>>>                        break;
>>>>>
>>>>> -             regmap_read(priv->regmap, MESON_SAR_ADC_FIFO_RD, 0);
>>>>> +             regmap_read(priv->regmap, MESON_SAR_ADC_FIFO_RD, NULL);
>>>>>        }
>>>>>   }
>>>>>
>>>>
>>>
>>> Regards,
>>> Martin
>>