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    SubjectRe: [lm-sensors] [PATCH] hwmon: (max1111) change sysfs interface to in[0-3]_input in millivolts
    On Wed, 9 Nov 2011 20:33:27 +0800, Eric Miao wrote:
    > On Wed, Nov 9, 2011 at 8:22 PM, Jean Delvare <khali@linux-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@linux-fr.org>
    > >> Signed-off-by: Eric Miao <eric.y.miao@gmail.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?

    I find the concept of LSB weight clear enough, but ultimately that's up
    to you, as long as the compiler actually optimizes it.

    --
    Jean Delvare
    --
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