linux-kernel - Re: [PATCH] i2c: imx-lpi2c: fix type char overflow issue when calculating the clock cycle

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Message-ID: <20230530185036.ggep3pv7booqtb6b@intel.intel>
Date:   Tue, 30 May 2023 20:50:36 +0200
From:   Andi Shyti <andi.shyti@...nel.org>
To:     carlos.song@....com
Cc:     aisheng.dong@....com, shawnguo@...nel.org, s.hauer@...gutronix.de,
        kernel@...gutronix.de, festevam@...il.com, xiaoning.wang@....com,
        haibo.chen@....com, linux-imx@....com, linux-i2c@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: imx-lpi2c: fix type char overflow issue when
 calculating the clock cycle

On Mon, May 29, 2023 at 04:02:51PM +0800, carlos.song@....com wrote:
> From: Clark Wang <xiaoning.wang@....com>
> 
> Claim clkhi and clklo as integer type to avoid possible calculation
> errors caused by data overflow.
> 
> Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
> Signed-off-by: Clark Wang <xiaoning.wang@....com>
> Signed-off-by: Carlos Song <carlos.song@....com>
> ---
>  drivers/i2c/busses/i2c-imx-lpi2c.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c b/drivers/i2c/busses/i2c-imx-lpi2c.c
> index 40a4420d4c12..7dd33564cbe1 100644
> --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> @@ -211,8 +211,8 @@ static void lpi2c_imx_stop(struct lpi2c_imx_struct *lpi2c_imx)
>  /* CLKLO = I2C_CLK_RATIO * CLKHI, SETHOLD = CLKHI, DATAVD = CLKHI/2 */
>  static int lpi2c_imx_config(struct lpi2c_imx_struct *lpi2c_imx)
>  {
> -	u8 prescale, filt, sethold, clkhi, clklo, datavd;
> -	unsigned int clk_rate, clk_cycle;
> +	u8 prescale, filt, sethold, datavd;
> +	unsigned int clk_rate, clk_cycle, clkhi, clklo;

looks OK.

Reviewed-by: Andi Shyti <andi.shyti@...nel.org> 

there is, though, another part I would take care of, this bit:

	clklo = clk_cycle - clkhi;
	if (clklo < 64)
		break;

It might be unlikely, but if "clk_cycle > clkhi" then all the
calculation. Do you mind adding a check:

	if (unlikely(clk_cycle > clkhi))
		break;

Andi

>  	enum lpi2c_imx_pincfg pincfg;
>  	unsigned int temp;
>  
> -- 
> 2.34.1
>