hid-xpadneo, rumble: Do not lose rumble strength while throttled

While the rumble thread is throttled, we may actually miss the peak
rumble strength resulting in an experience of rumbles with varying
strength when these are repeatedly sent by a game.

To work around this, we now accumulate the maximum strength set during
the throttle interval, then reset the accumulator when a rumble has
been sent to the controller.

Maybe-fixes: atar-axis#290
Signed-off-by: Kai Krakow <[email protected]>

hid-xpadneo/src/hid-xpadneo.c

@@ -242,6 +242,12 @@ static void xpadneo_ff_worker(struct work_struct *work)
 	/* shadow our current rumble values for the next cycle */
 	memcpy(&xdata->ff_shadow, &xdata->ff, sizeof(xdata->ff));
 
+	/* clear the magnitudes to properly accumulate the maximum values */
+	xdata->ff.magnitude_left = 0;
+	xdata->ff.magnitude_right = 0;
+	xdata->ff.magnitude_weak = 0;
+	xdata->ff.magnitude_strong = 0;
+
 	/*
 	 * throttle next command submission, the firmware doesn't like us to
 	 * send rumble data any faster
@@ -259,6 +265,7 @@ static void xpadneo_ff_worker(struct work_struct *work)
 		hid_warn(hdev, "failed to send FF report: %d\n", ret);
 }
 
+#define update_magnitude(m, v) m = (v) > 0 ? max(m, v) : 0
 static int xpadneo_ff_play(struct input_dev *dev, void *data, struct ff_effect *effect)
 {
 	enum {
@@ -369,12 +376,16 @@ static int xpadneo_ff_play(struct input_dev *dev, void *data, struct ff_effect *
 	spin_lock_irqsave(&xdata->ff_lock, flags);
 
 	/* calculate the physical magnitudes, scale from 16 bit to 0..100 */
-	xdata->ff.magnitude_strong = (u8)((strong * fraction_MAIN + S16_MAX) / U16_MAX);
-	xdata->ff.magnitude_weak = (u8)((weak * fraction_MAIN + S16_MAX) / U16_MAX);
+	update_magnitude(xdata->ff.magnitude_strong,
+			 (u8)((strong * fraction_MAIN + S16_MAX) / U16_MAX));
+	update_magnitude(xdata->ff.magnitude_weak,
+			 (u8)((weak * fraction_MAIN + S16_MAX) / U16_MAX));
 
 	/* calculate the physical magnitudes, scale from 16 bit to 0..100 */
-	xdata->ff.magnitude_left = (u8)((max_main * fraction_TL + S16_MAX) / U16_MAX);
-	xdata->ff.magnitude_right = (u8)((max_main * fraction_TR + S16_MAX) / U16_MAX);
+	update_magnitude(xdata->ff.magnitude_left,
+			 (u8)((max_main * fraction_TL + S16_MAX) / U16_MAX));
+	update_magnitude(xdata->ff.magnitude_right,
+			 (u8)((max_main * fraction_TR + S16_MAX) / U16_MAX));
 
 	/* synchronize: is our worker still scheduled? */
 	if (xdata->ff_scheduled) {