HID: nintendo: check analog user calibration for plausibility

Arne Wendt writes:
  Cheap clone controllers may (falsely) report as having a user
  calibration for the analog sticks in place, but return
  wrong/impossible values for the actual calibration data.
  In the present case at mine, the controller reports having a
  user calibration in place and successfully executes the read
  commands. The reported user calibration however is
  min = center = max = 0.

  This pull request addresses problems of this kind by checking the
  provided user calibration-data for plausibility (min < center < max)
  and falling back to the default values if implausible.

I'll note that I was experiencing a crash because of this bug when using
the GuliKit KingKong 2 controller. The crash manifests as a divide by
zero error in the kernel logs:
kernel: divide error: 0000 [#1] PREEMPT SMP NOPTI

Changes in v2:
 - Move the plausibility check to joycon_read_stick_calibration() and
   have that function return -EINVAL if the check fails.
 - In the plausibility check, change >= to ==. hid_field_extract() never
   returns a negative value, so a scenario involving min > center or
   center > max is impossible.
 - To reduce code duplication, move the code for setting default
   calibration values into a single function called
   joycon_use_default_calibration().

Changes in v3:
 - Unbreak warning string to conform to coding style.
 - Change joycon_use_default_calibration() to accept a struct hid_device
   pointer instead of a struct joycon_ctlr pointer.

Link: nicman23/dkms-hid-nintendo#25
Link: DanielOgorchock/linux#36
Co-authored-by: Arne Wendt <[email protected]>
Signed-off-by: Johnothan King <[email protected]>

drivers/hid/hid-nintendo.c

@@ -760,12 +760,31 @@ static int joycon_read_stick_calibration(struct joycon_ctlr *ctlr, u16 cal_addr,
 	cal_y->max = cal_y->center + y_max_above;
 	cal_y->min = cal_y->center - y_min_below;
 
-	return 0;
+	/* check if values are plausible */
+	if (cal_x->min == cal_x->center || cal_x->center == cal_x->max ||
+	    cal_y->min == cal_y->center || cal_y->center == cal_y->max)
+		ret = -EINVAL;
+
+	return ret;
 }
 
 static const u16 DFLT_STICK_CAL_CEN = 2000;
 static const u16 DFLT_STICK_CAL_MAX = 3500;
 static const u16 DFLT_STICK_CAL_MIN = 500;
+static void joycon_use_default_calibration(struct hid_device *hdev,
+					   struct joycon_stick_cal *cal_x,
+					   struct joycon_stick_cal *cal_y,
+					   const char *stick, int ret)
+{
+	hid_warn(hdev,
+		 "Failed to read %s stick cal, using defaults; e=%d\n", stick,
+		 ret);
+
+	cal_x->center = cal_y->center = DFLT_STICK_CAL_CEN;
+	cal_x->max = cal_y->max = DFLT_STICK_CAL_MAX;
+	cal_x->min = cal_y->min = DFLT_STICK_CAL_MIN;
+}
+
 static int joycon_request_calibration(struct joycon_ctlr *ctlr)
 {
 	u16 left_stick_addr = JC_CAL_FCT_DATA_LEFT_ADDR;
@@ -793,38 +812,24 @@ static int joycon_request_calibration(struct joycon_ctlr *ctlr)
 					    &ctlr->left_stick_cal_x,
 					    &ctlr->left_stick_cal_y,
 					    true);
-	if (ret) {
-		hid_warn(ctlr->hdev,
-			 "Failed to read left stick cal, using dflts; e=%d\n",
-			 ret);
-
-		ctlr->left_stick_cal_x.center = DFLT_STICK_CAL_CEN;
-		ctlr->left_stick_cal_x.max = DFLT_STICK_CAL_MAX;
-		ctlr->left_stick_cal_x.min = DFLT_STICK_CAL_MIN;
 
-		ctlr->left_stick_cal_y.center = DFLT_STICK_CAL_CEN;
-		ctlr->left_stick_cal_y.max = DFLT_STICK_CAL_MAX;
-		ctlr->left_stick_cal_y.min = DFLT_STICK_CAL_MIN;
-	}
+	if (ret)
+		joycon_use_default_calibration(ctlr->hdev,
+					       &ctlr->left_stick_cal_x,
+					       &ctlr->left_stick_cal_y,
+					       "left", ret);
 
 	/* read the right stick calibration data */
 	ret = joycon_read_stick_calibration(ctlr, right_stick_addr,
 					    &ctlr->right_stick_cal_x,
 					    &ctlr->right_stick_cal_y,
 					    false);
-	if (ret) {
-		hid_warn(ctlr->hdev,
-			 "Failed to read right stick cal, using dflts; e=%d\n",
-			 ret);
-
-		ctlr->right_stick_cal_x.center = DFLT_STICK_CAL_CEN;
-		ctlr->right_stick_cal_x.max = DFLT_STICK_CAL_MAX;
-		ctlr->right_stick_cal_x.min = DFLT_STICK_CAL_MIN;
 
-		ctlr->right_stick_cal_y.center = DFLT_STICK_CAL_CEN;
-		ctlr->right_stick_cal_y.max = DFLT_STICK_CAL_MAX;
-		ctlr->right_stick_cal_y.min = DFLT_STICK_CAL_MIN;
-	}
+	if (ret)
+		joycon_use_default_calibration(ctlr->hdev,
+					       &ctlr->right_stick_cal_x,
+					       &ctlr->right_stick_cal_y,
+					       "right", ret);
 
 	hid_dbg(ctlr->hdev, "calibration:\n"
 			    "l_x_c=%d l_x_max=%d l_x_min=%d\n"