Re: [lm-sensors] [PATCH] hwmon: (max1111) change sysfs interface toin[0-3]_input in millivolts

[Eric Miao]

On Wed, Nov 9, 2011 at 8:51 PM, Jean Delvare <khali@xxxxxxxxxxxx> wrote:
> On Wed, 9 Nov 2011 20:33:27 +0800, Eric Miao wrote:
>> On Wed, Nov 9, 2011 at 8:22 PM, Jean Delvare <khali@xxxxxxxxxxxx> wrote:
>> > Hi Eric,
>> >
>> > On Wed, Â9 Nov 2011 19:15:03 +0800, Eric Miao wrote:
>> >> This patch fixed the inconsistent max1111 sysfs interface as pointed
>> >> out by Jean Delvare:
>> >>
>> >> Â Â It was pointed to me that the max1111 driver doesn't implement the
>> >> Â Â standard sysfs interface for hwmon drivers (as described in
>> >> Â Â Documentation/hwmon/sysfs-interface). It exports files adc[0-3]_in,
>> >> Â Â which
>> >> Â Â aren't part of the standard interface. Presumably these should be
>> >> Â Â renamed to in[0-3]_input. Renaming them is probably not sufficient
>> >> Â Â though, as I see no scaling done in the driver. As the MAX1111 chip has
>> >> Â Â a documented full scale of 2.048V, I take it that the LSB of the ADC
>> >> Â Â has a weight of 8 mV. Exporting raw register values to user-space is
>> >> Â Â not OK.
>> >>
>> >> Reported-by: Jean Delvare <khali@xxxxxxxxxxxx>
>> >> Signed-off-by: Eric Miao <eric.y.miao@xxxxxxxxx>
>> >> ---
>> >> Âdrivers/hwmon/max1111.c | Â 13 +++++++------
>> >> Â1 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,
>> >> Â Â Â if (ret < 0)
>> >> Â Â Â Â Â Â Â return ret;
>> >>
>> >> - Â Â return sprintf(buf, "%d\n", ret);
>> >> + Â Â /* assume the reference voltage to be 2.048V */
>> >> + Â Â 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?
>
> I find the concept of LSB weight clear enough, but ultimately that's up
> to you, as long as the compiler actually optimizes it.

Sounds good, updated and resubmitted.
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