linux-kernel - Re: [PATCH 29/38] Input: touchscreen: atmel: remove invalid check

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Date:	Mon, 21 Sep 2015 10:10:41 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Andrzej Hajda <a.hajda@...sung.com>
Cc:	linux-kernel@...r.kernel.org,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Nick Dyer <nick.dyer@...ev.co.uk>, linux-input@...r.kernel.org
Subject: Re: [PATCH 29/38] Input: touchscreen: atmel: remove invalid check

Hi Andrzej,

On Mon, Sep 21, 2015 at 03:34:01PM +0200, Andrzej Hajda wrote:
> byte_offset is unsigned.
> 
> The problem has been detected using proposed semantic patch
> scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].
> 
> [1]: http://permalink.gmane.org/gmane.linux.kernel/2038576
> 
> Signed-off-by: Andrzej Hajda <a.hajda@...sung.com>
> ---
>  drivers/input/touchscreen/atmel_mxt_ts.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
> index c562205..c577f95 100644
> --- a/drivers/input/touchscreen/atmel_mxt_ts.c
> +++ b/drivers/input/touchscreen/atmel_mxt_ts.c
> @@ -1267,7 +1267,7 @@ static int mxt_prepare_cfg_mem(struct mxt_data *data,
>  
>  			byte_offset = reg + i - cfg_start_ofs;
>  
> -			if (byte_offset >= 0 && byte_offset < config_mem_size) {
> +			if (byte_offset < config_mem_size) {

I'd rather we kept the check as is: it documents the expected range even
if one of the checks is always true. If you search the archives you'll
find Linus has also pretty strong opinion about these checks actually
being useful from documenting POV.


>  				*(config_mem + byte_offset) = val;
>  			} else {
>  				dev_err(dev, "Bad object: reg:%d, T%d, ofs=%d\n",
> -- 
> 1.9.1
> 

Thanks.

-- 
Dmitry
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