Message-ID: <1500997958.6516.7.camel@perches.com>
Subject: Re: [PATCH] drm/stm: fix warning about multiplication in condition
From: Joe Perches <joe@perches.com>
To: Arnd Bergmann <arnd@arndb.de>, Yannick Fertre <yannick.fertre@st.com>,
        Philippe Cornu <philippe.cornu@st.com>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        Vincent Abriou <vincent.abriou@st.com>,
        David Airlie <airlied@linux.ie>
Cc: Neil Armstrong <narmstrong@baylibre.com>,
        Archit Taneja <architt@codeaurora.org>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Date: Tue, 25 Jul 2017 08:52:38 -0700
In-Reply-To: <20170725154130.332221-1-arnd@arndb.de>
References: <20170725154130.332221-1-arnd@arndb.de>
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On Tue, 2017-07-25 at 17:40 +0200, Arnd Bergmann wrote:
> gcc-7 complains about multiplying within a condition being
> suspicious:
> 
> drivers/gpu/drm/stm/dw_mipi_dsi-stm.c: In function 'dsi_pll_get_clkout_khz':
> drivers/gpu/drm/stm/dw_mipi_dsi-stm.c:117:10: error: '*' in boolean context, suggest '&&' instead [-Werror=int-in-bool-context]
> 
> The code here is correct, but can be easily rephrased to make
> that more obvious. I also swap out the error handling and the normal
> code path for clarity.

Thanks, the new code does read much better.

> diff --git a/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c b/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
[]
> @@ -113,11 +113,13 @@ static enum dsi_color dsi_color_from_mipi(enum mipi_dsi_pixel_format fmt)
>  
>  static int dsi_pll_get_clkout_khz(int clkin_khz, int idf, int ndiv, int odf)
>  {
> +	int divisor = idf * odf;
> +
>  	/* prevent from division by 0 */
> -	if (idf * odf)
> -		return DIV_ROUND_CLOSEST(clkin_khz * ndiv, idf * odf);
> +	if (!divisor)
> +		return 0;
>  
> -	return 0;
> +	return DIV_ROUND_CLOSEST(clkin_khz * ndiv, divisor);
>  }
>  
>  static int dsi_pll_get_params(int clkin_khz, int clkout_khz,