Re: [PATCH v2] ibmaem: Fix 64-bit division on 32-bit platforms

Carlos R. Mafra
2008-05-15T22:50:19Z

On Thu 15.May'08 at 14:18:09 -0700, Darrick J. Wong wrote:
> > To avoid these kind of doubts may I suggest using the time
> > conversion definitions of include/linux/time.h?
> >
> > It would be much easier to understand the intention with
> > NSEC_PER_SEC, USEC_PER_SEC etc (comments would also help)
>
> Ok, here's an updated version that makes the conversions a bit clearer.
> Tested and run on i386/x86-64.
> ---
> ibmaem: Fix 64-bit division on 32-bit platforms
>
> Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
> ---
>
> drivers/hwmon/ibmaem.c | 9 ++++++---
> 1 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/hwmon/ibmaem.c b/drivers/hwmon/ibmaem.c
> index 22fa7d6..3013492 100644
> --- a/drivers/hwmon/ibmaem.c
> +++ b/drivers/hwmon/ibmaem.c
> @@ -31,6 +31,8 @@
> #include <linux/idr.h>
> #include <linux/sched.h>
> #include <linux/platform_device.h>
> +#include <linux/math64.h>
> +#include <linux/time.h>
>
> #define REFRESH_INTERVAL (HZ)
> #define IPMI_TIMEOUT (30 * HZ)
> @@ -81,6 +83,7 @@
>
> #define AEM_DEFAULT_POWER_INTERVAL 1000
> #define AEM_MIN_POWER_INTERVAL 200
> +#define UJ_PER_MJ 1000L
>
> static DEFINE_IDR(aem_idr);
> static DEFINE_SPINLOCK(aem_idr_lock);
> @@ -841,7 +844,7 @@ static ssize_t aem_show_power(struct device *dev,
> {
> struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
> struct aem_data *data = dev_get_drvdata(dev);
> - u64 before, after, time;
> + u64 before, after, delta, time;
> signed long leftover;
> struct timespec b, a;
>
> @@ -864,9 +867,9 @@ static ssize_t aem_show_power(struct device *dev,
> mutex_unlock(&data->lock);
>
> time = timespec_to_ns(&a) - timespec_to_ns(&b);
> - time /= 1000;
> + delta = (after - before) * UJ_PER_MJ;
>
> - return sprintf(buf, "%llu\n", (after - before) * 1000000000 / time);
> + return sprintf(buf, "%llu\n", div64_u64(delta * NSEC_PER_SEC, time));
> }

Thanks!

Wow...so the power unit really is uW, which is a nice precision!