On Wed, May 08, 2019 at 11:34:50AM -0700, Florian Fainelli wrote: > On 5/8/19 11:32 AM, Guenter Roeck wrote: > > Hi Florian, > > > > On Wed, May 08, 2019 at 10:00:35AM -0700, Florian Fainelli wrote: > >> If the SCMI firmware implementation is reporting values in a scale that > >> is different from the HWMON units, we need to scale up or down the value > >> according to how far appart they are. > >> > >> Signed-off-by: Florian Fainelli <[email protected]> > >> --- > >> drivers/hwmon/scmi-hwmon.c | 46 ++++++++++++++++++++++++++++++++++++++ > >> 1 file changed, 46 insertions(+) > >> > >> diff --git a/drivers/hwmon/scmi-hwmon.c b/drivers/hwmon/scmi-hwmon.c > >> index a80183a488c5..4399372e2131 100644 > >> --- a/drivers/hwmon/scmi-hwmon.c > >> +++ b/drivers/hwmon/scmi-hwmon.c > >> @@ -7,6 +7,7 @@ > >> */ > >> > >> #include <linux/hwmon.h> > >> +#include <linux/limits.h> > >> #include <linux/module.h> > >> #include <linux/scmi_protocol.h> > >> #include <linux/slab.h> > >> @@ -18,6 +19,47 @@ struct scmi_sensors { > >> const struct scmi_sensor_info **info[hwmon_max]; > >> }; > >> > >> +static inline u64 __pow10(u8 x) > >> +{ > >> + u64 r = 1; > >> + > >> + while (x--) > >> + r *= 10; > >> + > >> + return r; > >> +} > >> + > >> +static int scmi_hwmon_scale(const struct scmi_sensor_info *sensor, u64 > >> *value) > >> +{ > >> + s8 scale = sensor->scale; > >> + u64 f; > >> + > >> + switch (sensor->type) { > >> + case TEMPERATURE_C: > >> + case VOLTAGE: > >> + case CURRENT: > >> + scale += 3; > >> + break; > >> + case POWER: > >> + case ENERGY: > >> + scale += 6; > >> + break; > >> + default: > >> + break; > >> + } > >> + > >> + f = __pow10(abs(scale)); > >> + if (f == U64_MAX) > >> + return -E2BIG; > > > > Unfortunately that is not how integer overflows work. > > > > A test program with increasing values of scale reports: > > > > 0: 1 > > ... > > 18: 1000000000000000000 > > 19: 10000000000000000000 > > 20: 7766279631452241920 > > 21: 3875820019684212736 > > 22: 1864712049423024128 > > 23: 200376420520689664 > > 24: 2003764205206896640 > > ... > > 61: 11529215046068469760 > > 62: 4611686018427387904 > > 63: 9223372036854775808 > > 64: 0 > > ... > > > > You'll have to check for abs(scale) > 19 if you want to report overflows. > > Yes silly me, my test program was flawed, thanks for pointing out that. > You are okay with returning E2BIG when we overflow?
Yes. Thanks, Guenter
