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SubjectRe: [PATCH v2] hwmon: (pmbus) Use 64bit math for DIRECT format values
On Mon, Nov 27, 2017 at 01:39:14PM -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 | 23 ++++++++++++++---------
> 1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index 52a58b8b6e1b..ff701502974a 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -21,6 +21,7 @@
>
> #include <linux/debugfs.h>
> #include <linux/kernel.h>
> +#include <linux/math64.h>
> #include <linux/module.h>
> #include <linux/init.h>
> #include <linux/err.h>
> @@ -499,8 +500,9 @@ 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 b, R;

Do b and R have to be s64 ? Seems excessive.

> + s32 m;
>
> m = data->info->m[sensor->class];
> b = data->info->b[sensor->class];
> @@ -528,11 +530,12 @@ static long pmbus_reg2data_direct(struct pmbus_data *data,
> R--;
> }
> while (R < 0) {
> - val = DIV_ROUND_CLOSEST(val, 10);
> + val = div_s64(val + 5LL, 10L); // round closest
> R++;
> }
>
> - return (val - b) / m;
> + val = div_s64(val - b, m);
> + return clamp_val(val, LONG_MIN, LONG_MAX);
> }
>
> /*
> @@ -656,7 +659,9 @@ 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 b, R;

Same question as above - do those have to be s64 ?

> + s32 m;
> + s64 val64 = val;
>
> m = data->info->m[sensor->class];
> b = data->info->b[sensor->class];
> @@ -673,18 +678,18 @@ 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);
> + val64 = div_s64(val64 + 5LL, 10L); // round closest
> R++;
> }
>
> - return val;
> + return (u16) clamp_val(val64, S16_MIN, S16_MAX);
> }
>
> static u16 pmbus_data2reg_vid(struct pmbus_data *data,
> --
> 2.15.0.417.g466bffb3ac-goog
>
> --
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