linux-kernel - Re: [PATCH 1/1] iio:adc: XADC: Set offset explicitly to zero on voltage channels

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Date:	Sun, 14 Jun 2015 11:15:19 +0800
From:	Gergely Imreh <imrehg@...il.com>
To:	Jonathan Cameron <jic23@...nel.org>
Cc:	michal.simek@...inx.com, linux-iio@...r.kernel.org,
	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel@...r.kernel.org, ola@...pteva.com,
	Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH 1/1] iio:adc: XADC: Set offset explicitly to zero on
 voltage channels

On 14 June 2015 at 02:30, Jonathan Cameron <jic23@...nel.org> wrote:
> On 11/06/15 09:22, Gergely Imreh wrote:
>> The Xilinx XADC driver has both a temperature channel and 8 voltage
>> channels. The voltage channels have no offset, but actually were still
>> set the same offset as the temperature channel. This did not cause
>> problems in /sys/bus/iio/ but can cause problems with other drivers
>> using iio data. For example iio-hwmon did return wrong voltage values
>> because of the offset.
>>
>> Change tested with the Parallella board.
>>
>> Signed-off-by: Gergely Imreh <imrehg@...il.com>
> Well spotted on the bug, but I think we are better off fixing this at the
> true source of the problem which is in drivers/iio/inkern.c
> iio_convert_raw_to_processed_unlocked which does a call to
> iio_channel_read(chan, &offset, NULL, IIO_CHAN_INFO_OFFSET) then uses
> the error return to check if the offset parameter is available. It should
> be checking that before making this call with a call to iio_channel_has_info.
>
> I don't suppose you could prepare a patch fixing that as you found the problem?

I'll check it out, and send an updated patch! Thanks for the pointers
to the core of the issue.

>
> If not I can fix it up sometime if no one else beats me to it.
>
> Thanks
>
> Jonathan
>> ---
>>  drivers/iio/adc/xilinx-xadc-core.c | 14 +++++++++++---
>>  1 file changed, 11 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/iio/adc/xilinx-xadc-core.c b/drivers/iio/adc/xilinx-xadc-core.c
>> index ab52be2..36efab7 100644
>> --- a/drivers/iio/adc/xilinx-xadc-core.c
>> +++ b/drivers/iio/adc/xilinx-xadc-core.c
>> @@ -877,9 +877,17 @@ static int xadc_read_raw(struct iio_dev *indio_dev,
>>                       return -EINVAL;
>>               }
>>       case IIO_CHAN_INFO_OFFSET:
>> -             /* Only the temperature channel has an offset */
>> -             *val = -((273150 << 12) / 503975);
>> -             return IIO_VAL_INT;
>> +             switch (chan->type) {
>> +             case IIO_VOLTAGE:
>> +                     *val = 0;
>> +                     return IIO_VAL_INT;
>> +             case IIO_TEMP:
>> +                     /* Only the temperature channel has an offset */
>> +                     *val = -((273150 << 12) / 503975);
>> +                     return IIO_VAL_INT;
>> +             default:
>> +                     return -EINVAL;
>> +             }
>>       case IIO_CHAN_INFO_SAMP_FREQ:
>>               ret = xadc_read_adc_reg(xadc, XADC_REG_CONF2, &val16);
>>               if (ret)
>>
>
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