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    SubjectRe: [lm-sensors] [PATCH] hwmon: sht15: Fix sht15_calc_temp interpolation function
    On 04/01/10 13:54, Jerome Oufella wrote:
    > ----- "Jean Delvare" <khali@linux-fr.org> wrote :
    >> May I suggest the more simple fix below?
    >>
    >> ---
    >> drivers/hwmon/sht15.c | 4 ++--
    >> 1 file changed, 2 insertions(+), 2 deletions(-)
    >>
    >> --- linux-2.6.34-rc3.orig/drivers/hwmon/sht15.c 2010-04-01
    >> 13:41:15.000000000 +0200
    >> +++ linux-2.6.34-rc3/drivers/hwmon/sht15.c 2010-04-01
    >> 13:41:55.000000000 +0200
    >> @@ -305,10 +305,10 @@ static inline int sht15_calc_temp(struct
    >> int d1 = 0;
    >> int i;
    >>
    >> - for (i = 1; i < ARRAY_SIZE(temppoints); i++)
    >> + for (i = ARRAY_SIZE(temppoints) - 1; i > 0 ;i--)
    >> /* Find pointer to interpolate */
    >> if (data->supply_uV > temppoints[i - 1].vdd) {
    >> - d1 = (data->supply_uV/1000 - temppoints[i - 1].vdd)
    >> + d1 = (data->supply_uV - temppoints[i - 1].vdd)
    >> * (temppoints[i].d1 - temppoints[i - 1].d1)
    >> / (temppoints[i].vdd - temppoints[i - 1].vdd)
    >> + temppoints[i - 1].d1;
    >>
    >> It leads to the same numbers as with Jerome's patch, with the
    >> advantages that 1* it is a much smaller change, more suitable for
    >> applying to stable kernels and 2* it avoids the magic constant number
    >> 10000.
    >>
    >> The "/1000" seems to be a relict of former times when
    >> temppoints[*].vdd
    >> was probably expressed in millivolt instead of microvolt. And the
    >> inverted loop iteration is obviously a bug.
    >>
    >> Note that in both cases, something should be done about values which
    >> are outside of the temppoints array. I don't know how likely these
    >> are,
    >> but they are seriously mishandled. For supply_uV values below
    >> temppoints[0].vdd, d1 defaults to 0, so no adjustment is done at all.
    >> temppoints[0].d1 would seem to be a much better default, if we don't
    >> want to do any interpolation in that case. For supply_uV values above
    >> temppoints[4].vdd, we do interpolate, which seems reasonable.
    >>
    >> Opinions?
    >>
    >> --
    >> Jean Delvare
    >
    > That's fine, it does a good job for me, in the expected voltage range.

    Seems sensible. I'm not quite sure but I think the code in question predates
    my involvement with the driver, so I'm guessing I never actually looked
    closely enough at it.

    Jonathan


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