linux-kernel - Re: GPU-DRM-i915: Delete an unnecessary check before the function call "pwm

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Date:	Fri, 06 Nov 2015 15:17:05 +0200
From:	Jani Nikula <jani.nikula@...ux.intel.com>
To:	SF Markus Elfring <elfring@...rs.sourceforge.net>,
	Daniel Vetter <daniel.vetter@...el.com>,
	David Airlie <airlied@...ux.ie>,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Cc:	LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org,
	Julia Lawall <julia.lawall@...6.fr>
Subject: Re: GPU-DRM-i915: Delete an unnecessary check before the function call "pwm_put"

On Fri, 06 Nov 2015, SF Markus Elfring <elfring@...rs.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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