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Re: [PATCH] GPU-DRM-i915: Delete an unnecessary check before the function call "pwm_put"

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  Re: [PATCH] GPU-DRM-i915: Delete an unnecessary check before the function call "pwm_put" Jani Nikula <jani.nikula@linux.intel.com> - 2015-11-06 13:50 +0100
    Re: GPU-DRM-i915: Delete an unnecessary check before the function  call "pwm_put" SF Markus Elfring <elfring@users.sourceforge.net> - 2015-11-06 14:00 +0100
      Re: GPU-DRM-i915: Delete an unnecessary check before the function call "pwm_put" Jani Nikula <jani.nikula@linux.intel.com> - 2015-11-06 14:20 +0100

#1263989 — Re: [PATCH] GPU-DRM-i915: Delete an unnecessary check before the function call "pwm_put"

On Fri, 06 Nov 2015, SF Markus Elfring <elfring@users.sourceforge.net> wrote:
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Fri, 6 Nov 2015 13:38:22 +0100
>
> The pwm_put() function tests whether its argument is NULL and then
> returns immediately. Thus the test around the call is not needed.

The compiler doesn't need it, but IMO it's useful documentation for
humans.

BR,
Jani.


>
> This issue was detected by using the Coccinelle software.
>
> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
>  drivers/gpu/drm/i915/intel_panel.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c
> index a24df35..3d8d913 100644
> --- a/drivers/gpu/drm/i915/intel_panel.c
> +++ b/drivers/gpu/drm/i915/intel_panel.c
> @@ -1729,8 +1729,7 @@ void intel_panel_destroy_backlight(struct drm_connector *connector)
>  	struct intel_panel *panel = &intel_connector->panel;
>  
>  	/* dispose of the pwm */
> -	if (panel->backlight.pwm)
> -		pwm_put(panel->backlight.pwm);
> +	pwm_put(panel->backlight.pwm);
>  
>  	panel->backlight.present = false;
>  }

-- 
Jani Nikula, Intel Open Source Technology Center
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#1263993 — Re: GPU-DRM-i915: Delete an unnecessary check before the function call "pwm_put"

>> The pwm_put() function tests whether its argument is NULL and then
>> returns immediately. Thus the test around the call is not needed.
> 
> The compiler doesn't need it, but IMO it's useful documentation for humans.

How do you think about to extend the explicit documentation for
the affected parameters in the Linux programming interfaces?

Regards,
Markus
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#1264004 — Re: GPU-DRM-i915: Delete an unnecessary check before the function call "pwm_put"

On Fri, 06 Nov 2015, SF Markus Elfring <elfring@users.sourceforge.net> wrote:
>>> The pwm_put() function tests whether its argument is NULL and then
>>> returns immediately. Thus the test around the call is not needed.
>> 
>> The compiler doesn't need it, but IMO it's useful documentation for humans.
>
> How do you think about to extend the explicit documentation for
> the affected parameters in the Linux programming interfaces?

The question is, while reading intel_panel.c, which one conveys the
reader better the idea that panel->backlight.pwm may be NULL for some
connectors:

a)	if (panel->backlight.pwm)
		pwm_put(panel->backlight.pwm);
	
b)	pwm_put(panel->backlight.pwm);

No amount of documentation in pwm_put() kernel-doc is going to help with
that. In most cases, panel->backlight.pwm is in fact NULL. IMO
unconditionally calling pwm_put() on it gives the reader the wrong idea.

Others may disagree.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center
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