linux-kernel - Re: [lm-sensors] [PATCH] hwmon: (max1111) change sysfs interface to in[0-3]

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Date:	Wed, 9 Nov 2011 20:33:27 +0800
From:	Eric Miao <eric.y.miao@...il.com>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	lm-sensors <lm-sensors@...sensors.org>
Subject: Re: [lm-sensors] [PATCH] hwmon: (max1111) change sysfs interface to
 in[0-3]_input in millivolts

On Wed, Nov 9, 2011 at 8:22 PM, Jean Delvare <khali@...ux-fr.org> wrote:
> Hi Eric,
>
> On Wed,  9 Nov 2011 19:15:03 +0800, Eric Miao wrote:
>> This patch fixed the inconsistent max1111 sysfs interface as pointed
>> out by Jean Delvare:
>>
>>     It was pointed to me that the max1111 driver doesn't implement the
>>     standard sysfs interface for hwmon drivers (as described in
>>     Documentation/hwmon/sysfs-interface). It exports files adc[0-3]_in,
>>     which
>>     aren't part of the standard interface. Presumably these should be
>>     renamed to in[0-3]_input. Renaming them is probably not sufficient
>>     though, as I see no scaling done in the driver. As the MAX1111 chip has
>>     a documented full scale of 2.048V, I take it that the LSB of the ADC
>>     has a weight of 8 mV. Exporting raw register values to user-space is
>>     not OK.
>>
>> Reported-by: Jean Delvare <khali@...ux-fr.org>
>> Signed-off-by: Eric Miao <eric.y.miao@...il.com>
>> ---
>>  drivers/hwmon/max1111.c |   13 +++++++------
>>  1 files changed, 7 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/hwmon/max1111.c b/drivers/hwmon/max1111.c
>> index c97b78e..0e9fcfd 100644
>> --- a/drivers/hwmon/max1111.c
>> +++ b/drivers/hwmon/max1111.c
>> @@ -106,11 +106,12 @@ static ssize_t show_adc(struct device *dev,
>>       if (ret < 0)
>>               return ret;
>>
>> -     return sprintf(buf, "%d\n", ret);
>> +     /* assume the reference voltage to be 2.048V */
>> +     return sprintf(buf, "%d\n", 2048 * 256 / ret);
>
> I bet you did not actually test your changes? ret == 0 would obviously
> crash the driver. The formula looks wrong anyway, should be 2048 *
> ret / 256. Or in short ret * 8, i.e. LSB weight of the ADC is 8 mV.
>

Oops, shame to death.

How about simply '2048 * ret / 256' to make it clear and leave it to
the compiler to optimize?

>>  }
>>
>>  #define MAX1111_ADC_ATTR(_id)                \
>> -     SENSOR_DEVICE_ATTR(adc##_id##_in, S_IRUGO, show_adc, NULL, _id)
>> +     SENSOR_DEVICE_ATTR(in##_id##_input, S_IRUGO, show_adc, NULL, _id)
>>
>>  static DEVICE_ATTR(name, S_IRUGO, show_name, NULL);
>>  static MAX1111_ADC_ATTR(0);
>> @@ -120,10 +121,10 @@ static MAX1111_ADC_ATTR(3);
>>
>>  static struct attribute *max1111_attributes[] = {
>>       &dev_attr_name.attr,
>> -     &sensor_dev_attr_adc0_in.dev_attr.attr,
>> -     &sensor_dev_attr_adc1_in.dev_attr.attr,
>> -     &sensor_dev_attr_adc2_in.dev_attr.attr,
>> -     &sensor_dev_attr_adc3_in.dev_attr.attr,
>> +     &sensor_dev_attr_in0_input.dev_attr.attr,
>> +     &sensor_dev_attr_in1_input.dev_attr.attr,
>> +     &sensor_dev_attr_in2_input.dev_attr.attr,
>> +     &sensor_dev_attr_in3_input.dev_attr.attr,
>>       NULL,
>>  };
>>
>
> The rest of the changes look good.
>
> --
> Jean Delvare
>
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