Input: preallocate memory to hold event values

Preallocate memory for holding event values (input_dev->vals) so that
there is no need to check if it was allocated or not in the event
processing code.

The amount of memory will be adjusted after input device has been fully
set up upon registering device with the input core.

Reviewed-by: Jeff LaBundy <jeff@labundy.com>
Reviewed-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240703213756.3375978-7-dmitry.torokhov@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: dtor

drivers/input/input.c

@@ -323,9 +323,6 @@ static void input_event_dispose(struct input_dev *dev, int disposition,
 	if ((disposition & INPUT_PASS_TO_DEVICE) && dev->event)
 		dev->event(dev, type, code, value);
 
-	if (!dev->vals)
-		return;
-
 	if (disposition & INPUT_PASS_TO_HANDLERS) {
 		struct input_value *v;
 
@@ -1985,6 +1982,18 @@ struct input_dev *input_allocate_device(void)
 	if (!dev)
 		return NULL;
 
+	/*
+	 * Start with space for SYN_REPORT + 7 EV_KEY/EV_MSC events + 2 spare,
+	 * see input_estimate_events_per_packet(). We will tune the number
+	 * when we register the device.
+	 */
+	dev->max_vals = 10;
+	dev->vals = kcalloc(dev->max_vals, sizeof(*dev->vals), GFP_KERNEL);
+	if (!dev->vals) {
+		kfree(dev);
+		return NULL;
+	}
+
 	mutex_init(&dev->mutex);
 	spin_lock_init(&dev->event_lock);
 	timer_setup(&dev->timer, NULL, 0);
@@ -2344,6 +2353,35 @@ bool input_device_enabled(struct input_dev *dev)
 }
 EXPORT_SYMBOL_GPL(input_device_enabled);
 
+static int input_device_tune_vals(struct input_dev *dev)
+{
+	struct input_value *vals;
+	unsigned int packet_size;
+	unsigned int max_vals;
+
+	packet_size = input_estimate_events_per_packet(dev);
+	if (dev->hint_events_per_packet < packet_size)
+		dev->hint_events_per_packet = packet_size;
+
+	max_vals = dev->hint_events_per_packet + 2;
+	if (dev->max_vals >= max_vals)
+		return 0;
+
+	vals = kcalloc(max_vals, sizeof(*vals), GFP_KERNEL);
+	if (!vals)
+		return -ENOMEM;
+
+	spin_lock_irq(&dev->event_lock);
+	dev->max_vals = max_vals;
+	swap(dev->vals, vals);
+	spin_unlock_irq(&dev->event_lock);
+
+	/* Because of swap() above, this frees the old vals memory */
+	kfree(vals);
+
+	return 0;
+}
+
 /**
  * input_register_device - register device with input core
  * @dev: device to be registered
@@ -2371,7 +2409,6 @@ int input_register_device(struct input_dev *dev)
 {
 	struct input_devres *devres = NULL;
 	struct input_handler *handler;
-	unsigned int packet_size;
 	const char *path;
 	int error;
 
@@ -2399,16 +2436,9 @@ int input_register_device(struct input_dev *dev)
 	/* Make sure that bitmasks not mentioned in dev->evbit are clean. */
 	input_cleanse_bitmasks(dev);
 
-	packet_size = input_estimate_events_per_packet(dev);
-	if (dev->hint_events_per_packet < packet_size)
-		dev->hint_events_per_packet = packet_size;
-
-	dev->max_vals = dev->hint_events_per_packet + 2;
-	dev->vals = kcalloc(dev->max_vals, sizeof(*dev->vals), GFP_KERNEL);
-	if (!dev->vals) {
-		error = -ENOMEM;
+	error = input_device_tune_vals(dev);
+	if (error)
 		goto err_devres_free;
-	}
 
 	/*
 	 * If delay and period are pre-set by the driver, then autorepeating
@@ -2428,7 +2458,7 @@ int input_register_device(struct input_dev *dev)
 
 	error = device_add(&dev->dev);
 	if (error)
-		goto err_free_vals;
+		goto err_devres_free;
 
 	path = kobject_get_path(&dev->dev.kobj, GFP_KERNEL);
 	pr_info("%s as %s\n",
@@ -2458,9 +2488,6 @@ int input_register_device(struct input_dev *dev)
 
 err_device_del:
 	device_del(&dev->dev);
-err_free_vals:
-	kfree(dev->vals);
-	dev->vals = NULL;
 err_devres_free:
 	devres_free(devres);
 	return error;