[PATCH v2 23/33] HID: logitech-hidpp: index G920 force-feedback slots by effect ID

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

The G920 driver previously maintained an effect_ids array indexed by
hardware slot minus 1 to store the associated input effect ID. Locating
the hardware slot assigned to an effect ID required iterating through
the array in hidpp_ff_find_effect() on every playback, destroy, or
update request.

Reverse the mapping by storing an array of hardware slot numbers indexed
directly by the 0-based input effect ID. Because input effect IDs are
allocated in the range 0 to num_effects - 1, looking up a slot becomes
an O(1) array access and hidpp_ff_find_effect() can be removed. Sizing
the array as u8 slots[] also allows zero to represent an unassigned slot
because hardware slot numbers returned by the device are non-zero,
eliminating the need to initialize entries to -1.

In g920_get_config(), deduct the reserved autocenter slot count when
storing num_effects so that data.num_effects reflects the number of
user-assignable effect slots and can be passed directly to
input_ff_create().

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/hid/hid-logitech-hidpp.c | 31 +++++++++----------------------
 1 file changed, 9 insertions(+), 22 deletions(-)

diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
index ceaa57af6eab..9526286ba406 100644
--- a/drivers/hid/hid-logitech-hidpp.c
+++ b/drivers/hid/hid-logitech-hidpp.c
@@ -2344,7 +2344,7 @@ struct hidpp_ff_private_data {
 	struct workqueue_struct *wq;
 	atomic_t workqueue_size;
 	u8 num_effects;
-	int effect_ids[] __counted_by(num_effects);
+	u8 slots[] __counted_by(num_effects);
 };
 
 struct g920_data {
@@ -2401,17 +2401,6 @@ static const char *HIDPP_FF_CONDITION_NAMES[] = {
 };
 
 
-static u8 hidpp_ff_find_effect(struct hidpp_ff_private_data *data, int effect_id)
-{
-	int i;
-
-	for (i = 0; i < data->num_effects; i++)
-		if (data->effect_ids[i] == effect_id)
-			return i+1;
-
-	return 0;
-}
-
 static void hidpp_ff_work_handler(struct work_struct *w)
 {
 	struct hidpp_ff_work_data *wd = container_of(w, struct hidpp_ff_work_data, work);
@@ -2431,7 +2420,7 @@ static void hidpp_ff_work_handler(struct work_struct *w)
 		break;
 	default:
 		/* find current slot for effect */
-		wd->params[0] = hidpp_ff_find_effect(data, wd->effect_id);
+		wd->params[0] = data->slots[wd->effect_id];
 		break;
 	}
 
@@ -2449,10 +2438,10 @@ static void hidpp_ff_work_handler(struct work_struct *w)
 	switch (wd->command) {
 	case HIDPP_FF_DOWNLOAD_EFFECT:
 		slot = response.fap.params[0];
-		if (slot > 0 && slot <= data->num_effects) {
+		if (slot > 0) {
 			if (wd->effect_id >= 0)
 				/* regular effect uploaded */
-				data->effect_ids[slot-1] = wd->effect_id;
+				data->slots[wd->effect_id] = slot;
 			else if (wd->effect_id >= HIDPP_FF_EFFECTID_AUTOCENTER)
 				/* autocenter spring uploaded */
 				g920->slot_autocenter = slot;
@@ -2460,10 +2449,10 @@ static void hidpp_ff_work_handler(struct work_struct *w)
 		break;
 	case HIDPP_FF_DESTROY_EFFECT:
 		slot = wd->params[0];
-		if (slot > 0 && slot <= data->num_effects) {
+		if (slot > 0) {
 			if (wd->effect_id >= 0)
 				/* regular effect destroyed */
-				data->effect_ids[slot-1] = -1;
+				data->slots[wd->effect_id] = 0;
 			else if (wd->effect_id >= HIDPP_FF_EFFECTID_AUTOCENTER)
 				/* autocenter spring destroyed */
 				g920->slot_autocenter = 0;
@@ -2855,14 +2844,12 @@ static int hidpp_ff_init(struct hidpp_device *hidpp, struct input_dev *dev)
 	}
 
 	struct hidpp_ff_private_data *data __free(kfree) =
-		kzalloc_flex(*data, effect_ids, num_slots);
+		kzalloc_flex(*data, slots, num_slots);
 	if (!data)
 		return -ENOMEM;
 
 	data->hidpp = hidpp;
 	data->num_effects = num_slots;
-	for (j = 0; j < num_slots; j++)
-		data->effect_ids[j] = -1;
 
 	/* init the hardware command queue */
 	atomic_set(&data->workqueue_size, 0);
@@ -2883,7 +2870,7 @@ static int hidpp_ff_init(struct hidpp_device *hidpp, struct input_dev *dev)
 		for (j = 0; hidpp_ff_effects_v2[j] >= 0; j++)
 			set_bit(hidpp_ff_effects_v2[j], dev->ffbit);
 
-	error = input_ff_create(dev, num_slots - HIDPP_FF_RESERVED_SLOTS);
+	error = input_ff_create(dev, num_slots);
 	if (error) {
 		hid_err(hid, "Failed to create FF device!\n");
 		bitmap_zero(dev->ffbit, FF_CNT);
@@ -3461,7 +3448,7 @@ static int g920_get_config(struct hidpp_device *hidpp)
 		return -EINVAL;
 	}
 
-	data.num_effects = response.fap.params[0];
+	data.num_effects = response.fap.params[0] - HIDPP_FF_RESERVED_SLOTS;
 
 	/* reset all forces */
 	ret = hidpp_send_fap_command_sync(hidpp, data.feature_index,

-- 
2.56.0.542.g3ef89b7020-goog