linux-kernel - Re: [PATCH 2/3] Input: alps: drop unlikely before IS_ERR_OR

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Message-ID: <20151001073019.GE1829@pali>
Date:	Thu, 1 Oct 2015 09:30:19 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Geliang Tang <geliangtang@....com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Masaki Ota <masaki.ota@...alps.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] Input: alps: drop unlikely before IS_ERR_OR_NULL

On Thursday 01 October 2015 10:55:30 Geliang Tang wrote:
> IS_ERR_OR_NULL already contain an unlikely compiler flag. Drop it.
> 
> Signed-off-by: Geliang Tang <geliangtang@....com>
> ---
>  drivers/input/mouse/alps.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
> index 4d24686..b4f146a 100644
> --- a/drivers/input/mouse/alps.c
> +++ b/drivers/input/mouse/alps.c
> @@ -1367,7 +1367,7 @@ static void alps_report_bare_ps2_packet(struct psmouse *psmouse,
>  		/* On V2 devices the DualPoint Stick reports bare packets */
>  		dev = priv->dev2;
>  		dev2 = psmouse->dev;
> -	} else if (unlikely(IS_ERR_OR_NULL(priv->dev3))) {
> +	} else if (IS_ERR_OR_NULL(priv->dev3)) {
>  		/* Register dev3 mouse if we received PS/2 packet first time */
>  		if (!IS_ERR(priv->dev3))
>  			psmouse_queue_work(psmouse, &priv->dev3_register_work,

Hm... I do not like this change. If I read code

 if (unlikely(IS_ERR_OR_NULL(priv->dev3)))

then I know that it is really unlikely that condition will be truth and
so this is some case of error/exception or something that normally does
not happen too much.

But if I read code

 if (IS_ERR_OR_NULL(priv->dev3))

I know nothing about chance that this condition will be truth. Explicit
unlikely in previous example give me more information.

-- 
Pali Rohár
pali.rohar@...il.com
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