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SubjectRe: [PATCH] hwmon: (pmbus) Use 64bit math for DIRECT format values
On Wed, Nov 22, 2017 at 02:08:43PM -0800, Robert Lippert wrote:
> Power values in the 100s of watt range can easily blow past
> 32bit math limits when processing everything in microwatts.
>
> Use 64bit math instead to avoid these issues on common 32bit ARM
> BMC platforms.
>
> Signed-off-by: Robert Lippert <rlippert@google.com>
> ---
> drivers/hwmon/pmbus/pmbus_core.c | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index 52a58b8b6e1b..f4efea9f282e 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -499,8 +499,8 @@ static long pmbus_reg2data_linear(struct pmbus_data *data,
> static long pmbus_reg2data_direct(struct pmbus_data *data,
> struct pmbus_sensor *sensor)
> {
> - long val = (s16) sensor->data;
> - long m, b, R;
> + s64 val = (s16) sensor->data;
> + s64 m, b, R;
>
> m = data->info->m[sensor->class];
> b = data->info->b[sensor->class];
> @@ -528,11 +528,13 @@ static long pmbus_reg2data_direct(struct pmbus_data *data,
> R--;
> }
> while (R < 0) {
> - val = DIV_ROUND_CLOSEST(val, 10);
> + do_div(val, 10);

Any reason to not use DIV_ROUND_CLOSEST_ULL ?

> R++;
> }
>
> - return (val - b) / m;
> + val = val - b;
> + do_div(val, m);
> + return val;

Can this overflow ?

> }
>
> /*
> @@ -656,7 +658,8 @@ static u16 pmbus_data2reg_linear(struct pmbus_data *data,
> static u16 pmbus_data2reg_direct(struct pmbus_data *data,
> struct pmbus_sensor *sensor, long val)
> {
> - long m, b, R;
> + s64 m, b, R;
> + s64 val64 = val;
>
> m = data->info->m[sensor->class];
> b = data->info->b[sensor->class];
> @@ -673,18 +676,18 @@ static u16 pmbus_data2reg_direct(struct pmbus_data *data,
> R -= 3; /* Adjust R and b for data in milli-units */
> b *= 1000;
> }
> - val = val * m + b;
> + val64 = val64 * m + b;
>
> while (R > 0) {
> - val *= 10;
> + val64 *= 10;
> R--;
> }
> while (R < 0) {
> - val = DIV_ROUND_CLOSEST(val, 10);
> + do_div(val64, 10);

Same here.

> R++;
> }
>
> - return val;
> + return (u16) val64;

Can this overflow ?

> }
>
> static u16 pmbus_data2reg_vid(struct pmbus_data *data,
> --
> 2.15.0.448.gf294e3d99a-goog
>

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