Re: [PATCH 1/4] kernel.h: Implement DIV_ROUND_CLOSEST_ULL

[Alex Elder <elder@ieee.org>]

On 03/20/2015 06:14 AM, Javi Merino wrote:
> We have grown a number of different implementations of
> DIV_ROUND_CLOSEST_ULL throughout the kernel.  Move the i915 one to
> kernel.h so that it can be reused.
> 
> Cc: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Darrick J. Wong <djwong@us.ibm.com>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Javi Merino <javi.merino@arm.com>
> ---
>  drivers/gpu/drm/i915/intel_drv.h |  4 +---
>  include/linux/kernel.h           | 11 +++++++++++
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index eef79ccd0b7c..346e28fdd7dd 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -28,6 +28,7 @@
>  #include <linux/async.h>
>  #include <linux/i2c.h>
>  #include <linux/hdmi.h>
> +#include <linux/kernel.h>
>  #include <drm/i915_drm.h>
>  #include "i915_drv.h"
>  #include <drm/drm_crtc.h>
> @@ -36,9 +37,6 @@
>  #include <drm/drm_dp_mst_helper.h>
>  #include <drm/drm_rect.h>
>  
> -#define DIV_ROUND_CLOSEST_ULL(ll, d)	\
> -({ unsigned long long _tmp = (ll)+(d)/2; do_div(_tmp, d); _tmp; })
> -
>  /**
>   * _wait_for - magic (register) wait macro
>   *
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index d6d630d31ef3..f7d744e9d275 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -103,6 +103,17 @@
>  		(((__x) - ((__d) / 2)) / (__d));	\
>  }							\
>  )
> +/*
> + * Same as above but for u64 dividends.  divisor must be a 32-bit
> + * number.
> + */
> +#define DIV_ROUND_CLOSEST_ULL(x, divisor)(		\
> +{							\
> +	unsigned long long _tmp = (x) + (divisor) / 2;	\
> +	do_div(_tmp, divisor);				\
> +	_tmp;						\
> +}							\
> +)

Since you are stipulating the types of the arguments, this
should be defined as a static inline function instead.

DIV_ROUND_CLOSEST() could conceivably handle a 64-bit
dividend properly, although that macro is already a bit
hard to look at.

					-Alex

>  
>  /*
>   * Multiplies an integer by a fraction, while avoiding unnecessary
>