linux-kernel - Re: [PATCH 4/6] pwm: pwm-lpc18xx-sct: test clock rate to avoid division by 0

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Message-ID: <CAGhQ9VzQLfhT4erDam_69-Zf4vp3gzKx+jbanXM8Ky+fmG=6EQ@mail.gmail.com>
Date:	Wed, 2 Mar 2016 23:44:02 +0100
From:	Joachim Eastwood <manabian@...il.com>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-renesas-soc@...r.kernel.org,
	Thierry Reding <thierry.reding@...il.com>,
	linux-pwm@...r.kernel.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"Ariel D'Alessandro" <ariel@...guardiasur.com.ar>
Subject: Re: [PATCH 4/6] pwm: pwm-lpc18xx-sct: test clock rate to avoid
 division by 0

Hi Wolfram,

On 2 March 2016 at 23:33, Wolfram Sang <wsa@...-dreams.de> wrote:
> From: Wolfram Sang <wsa+renesas@...g-engineering.com>
>
> The clk API may return 0 on clk_get_rate, so we should check the result before
> using it as a divisor.
>
> Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
> ---
>
> Should go individually via subsystem tree.
>
>  drivers/pwm/pwm-lpc18xx-sct.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/pwm/pwm-lpc18xx-sct.c b/drivers/pwm/pwm-lpc18xx-sct.c
> index 9163085101bc94..6487962c355c03 100644
> --- a/drivers/pwm/pwm-lpc18xx-sct.c
> +++ b/drivers/pwm/pwm-lpc18xx-sct.c
> @@ -360,6 +360,8 @@ static int lpc18xx_pwm_probe(struct platform_device *pdev)
>         }
>
>         lpc18xx_pwm->clk_rate = clk_get_rate(lpc18xx_pwm->pwm_clk);
> +       if (!lpc18xx_pwm->clk_rate)
> +               return -EINVAL;

This needs to be:
if (!lpc18xx_pwm->clk_rate) {
    ret = -EINVAL;
    goto disable_pwmclk;
}

I would also prefer an explicit check against 0 here. ie.:
'lpc18xx_pwm->clk_rate == 0'
A dev_err() message would also be nice to have.


regards,
Joachim Eastwood