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

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Message-Id: <20230318133010.1285202-1-Jason@zx2c4.com>
Date:   Sat, 18 Mar 2023 14:30:10 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     dmitry.torokhov@...il.com, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org, regressions@...ts.linux.dev
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>, stable@...r.kernel.org,
        regressions@...mhuis.info, barry@...sagefor.me.uk
Subject: [PATCH] Input: focaltech - use explicitly signed char type

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.

 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];
 	}
 }
 
-- 
2.40.0