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

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Message-ID: <20080515224914.GA27674@beyonder.ift.unesp.br>
Date:	Thu, 15 May 2008 19:49:14 -0300
From:	"Carlos R. Mafra" <crmafra2@...il.com>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Adrian Bunk <bunk@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	mhoffman@...htlink.com, linux-kernel@...r.kernel.org,
	lm-sensors@...sensors.org
Subject: Re: [PATCH v2] ibmaem: Fix 64-bit division on 32-bit platforms

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@...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! 
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