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

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Message-ID: <20111109132238.0a35ccee@endymion.delvare>
Date:	Wed, 9 Nov 2011 13:22:38 +0100
From:	Jean Delvare <khali@...ux-fr.org>
To:	Eric Miao <eric.y.miao@...il.com>
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

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.

>  }
>  
>  #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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