HID: nintendo: Prevent divide-by-zero on code

It was reported [0] that adding a generic joycon to the system caused
a kernel crash on Steam Deck, with the below panic spew:

divide error: 0000 [linuxppc#1] PREEMPT SMP NOPTI
[...]
Hardware name: Valve Jupiter/Jupiter, BIOS F7A0119 10/24/2023
RIP: 0010:nintendo_hid_event+0x340/0xcc1 [hid_nintendo]
[...]
Call Trace:
 [...]
 ? exc_divide_error+0x38/0x50
 ? nintendo_hid_event+0x340/0xcc1 [hid_nintendo]
 ? asm_exc_divide_error+0x1a/0x20
 ? nintendo_hid_event+0x307/0xcc1 [hid_nintendo]
 hid_input_report+0x143/0x160
 hidp_session_run+0x1ce/0x700 [hidp]

Since it's a divide-by-0 error, by tracking the code for potential
denominator issues, we've spotted 2 places in which this could happen;
so let's guard against the possibility and log in the kernel if the
condition happens. This is specially useful since some data that
fills some denominators are read from the joycon HW in some cases,
increasing the potential for flaws.

[0] ValveSoftware/SteamOS#1070

Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Tested-by: Sam Lantinga <slouken@libsdl.org>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

drivers/hid/hid-nintendo.c

@@ -927,14 +927,27 @@ static int joycon_request_calibration(struct joycon_ctlr *ctlr)
  */
 static void joycon_calc_imu_cal_divisors(struct joycon_ctlr *ctlr)
 {
-	int i;
+	int i, divz = 0;
 
 	for (i = 0; i < 3; i++) {
 		ctlr->imu_cal_accel_divisor[i] = ctlr->accel_cal.scale[i] -
 						ctlr->accel_cal.offset[i];
 		ctlr->imu_cal_gyro_divisor[i] = ctlr->gyro_cal.scale[i] -
 						ctlr->gyro_cal.offset[i];
+
+		if (ctlr->imu_cal_accel_divisor[i] == 0) {
+			ctlr->imu_cal_accel_divisor[i] = 1;
+			divz++;
+		}
+
+		if (ctlr->imu_cal_gyro_divisor[i] == 0) {
+			ctlr->imu_cal_gyro_divisor[i] = 1;
+			divz++;
+		}
 	}
+
+	if (divz)
+		hid_warn(ctlr->hdev, "inaccurate IMU divisors (%d)\n", divz);
 }
 
 static const s16 DFLT_ACCEL_OFFSET /*= 0*/;
@@ -1163,16 +1176,16 @@ static void joycon_parse_imu_report(struct joycon_ctlr *ctlr,
 		    JC_IMU_SAMPLES_PER_DELTA_AVG) {
 			ctlr->imu_avg_delta_ms = ctlr->imu_delta_samples_sum /
 						 ctlr->imu_delta_samples_count;
-			/* don't ever want divide by zero shenanigans */
-			if (ctlr->imu_avg_delta_ms == 0) {
-				ctlr->imu_avg_delta_ms = 1;
-				hid_warn(ctlr->hdev,
-					 "calculated avg imu delta of 0\n");
-			}
 			ctlr->imu_delta_samples_count = 0;
 			ctlr->imu_delta_samples_sum = 0;
 		}
 
+		/* don't ever want divide by zero shenanigans */
+		if (ctlr->imu_avg_delta_ms == 0) {
+			ctlr->imu_avg_delta_ms = 1;
+			hid_warn(ctlr->hdev, "calculated avg imu delta of 0\n");
+		}
+
 		/* useful for debugging IMU sample rate */
 		hid_dbg(ctlr->hdev,
 			"imu_report: ms=%u last_ms=%u delta=%u avg_delta=%u\n",