linux-kernel - Re: v4.9-rc1: smiapp divides by zero

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Date:   Sun, 23 Oct 2016 17:09:11 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Pavel Machek <pavel@....cz>
Cc:     Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>, sre@...nel.org,
        pali.rohar@...il.com, linux-media@...r.kernel.org,
        galak@...eaurora.org, mchehab@....samsung.com,
        linux-kernel@...r.kernel.org
Subject: Re: v4.9-rc1: smiapp divides by zero

Hi Pavel,

On Sun, Oct 23, 2016 at 12:22:13PM +0200, Pavel Machek wrote:
> Hi!
> 
> I tried to update camera code on n900 to v4.9-rc1, and I'm getting
> some divide by zero, that eventually cascades into fcam-dev not
> working.
> 
> mul is zero in my testing, resulting in divide by zero.
> 
> (Note that this is going from my patched camera-v4.8 tree to
> camera-v4.9 tree.)
> 
> Best regards,
> 								Pavel
> 
> diff --git a/drivers/media/i2c/smiapp-pll.c b/drivers/media/i2c/smiapp-pll.c
> index 5ad1edb..e0a6edd 100644
> --- a/drivers/media/i2c/smiapp-pll.c
> +++ b/drivers/media/i2c/smiapp-pll.c
> @@ -16,6 +16,8 @@
>   * General Public License for more details.
>   */
>  
> +#define DEBUG
> +
>  #include <linux/device.h>
>  #include <linux/gcd.h>
>  #include <linux/lcm.h>
> @@ -457,6 +459,10 @@ int smiapp_pll_calculate(struct device *dev,
>  	i = gcd(pll->pll_op_clk_freq_hz, pll->ext_clk_freq_hz);
>  	mul = div_u64(pll->pll_op_clk_freq_hz, i);
>  	div = pll->ext_clk_freq_hz / i;
> +	if (!mul) {

Something must be very wrong if you get here.

What are the values of pll->pll_op_clk_freq_hz and pll->ext_clk_freq_hz?
Or... what does dmesg say?

> +		dev_err(dev, "forcing mul to 1\n");
> +		mul = 1;
> +	}
>  	dev_dbg(dev, "mul %u / div %u\n", mul, div);
>  
>  	min_pre_pll_clk_div =
> 

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@....fi	XMPP: sailus@...iisi.org.uk