linux-kernel - Re: [PATCH] Input: focaltech - use explicitly signed char type

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Date:   Sat, 18 Mar 2023 17:43:06 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>, dmitry.torokhov@...il.com,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        regressions@...ts.linux.dev
Cc:     stable@...r.kernel.org, regressions@...mhuis.info,
        barry@...sagefor.me.uk
Subject: Re: [PATCH] Input: focaltech - use explicitly signed char type

Hi,

On 3/18/23 14:30, Jason A. Donenfeld wrote:
> The recent change of -funsigned-char causes additions of negative
> numbers to become additions of large positive numbers, leading to wrong
> calculations of mouse movement. Change these casts to be explictly
> signed, to take into account negative offsets.
> 
> Fixes: 3bc753c06dd0 ("kbuild: treat char as always unsigned")
> Cc: stable@...r.kernel.org
> Cc: regressions@...mhuis.info
> Cc: barry@...sagefor.me.uk
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
> Wrote this patch from my phone, untested, so it would be nice if
> somebody with hardware could confirm it works.

Thanks, patch looks good to me:

Reviewed-by: Hans de Goede <hdegoede@...hat.com>

Regards,

Hans


> 
>  drivers/input/mouse/focaltech.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/input/mouse/focaltech.c b/drivers/input/mouse/focaltech.c
> index 6fd5fff0cbff..3dbad0d8e8c9 100644
> --- a/drivers/input/mouse/focaltech.c
> +++ b/drivers/input/mouse/focaltech.c
> @@ -202,8 +202,8 @@ static void focaltech_process_rel_packet(struct psmouse *psmouse,
>  	state->pressed = packet[0] >> 7;
>  	finger1 = ((packet[0] >> 4) & 0x7) - 1;
>  	if (finger1 < FOC_MAX_FINGERS) {
> -		state->fingers[finger1].x += (char)packet[1];
> -		state->fingers[finger1].y += (char)packet[2];
> +		state->fingers[finger1].x += (signed char)packet[1];
> +		state->fingers[finger1].y += (signed char)packet[2];
>  	} else {
>  		psmouse_err(psmouse, "First finger in rel packet invalid: %d\n",
>  			    finger1);
> @@ -218,8 +218,8 @@ static void focaltech_process_rel_packet(struct psmouse *psmouse,
>  	 */
>  	finger2 = ((packet[3] >> 4) & 0x7) - 1;
>  	if (finger2 < FOC_MAX_FINGERS) {
> -		state->fingers[finger2].x += (char)packet[4];
> -		state->fingers[finger2].y += (char)packet[5];
> +		state->fingers[finger2].x += (signed char)packet[4];
> +		state->fingers[finger2].y += (signed char)packet[5];
>  	}
>  }
>