2 files changed, 28 insertions, 2 deletions

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index cff7bf9351a8..30836c05edd7 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -10,7 +10,8 @@
 
 #define EVDEV_MINOR_BASE        64
 #define EVDEV_MINORS            32
-#define EVDEV_MIN_BUFFER_SIZE   64
+#define EVDEV_MIN_BUFFER_SIZE   64U
+#define EVDEV_BUF_PACKETS       8
 
 #include <linux/poll.h>
 #include <linux/sched.h>
@@ -245,7 +246,11 @@ static int evdev_release(struct inode *inode, struct file *file)
 
 static unsigned int evdev_compute_buffer_size(struct input_dev *dev)
 {
-        return EVDEV_MIN_BUFFER_SIZE;
+        unsigned int n_events =
+                max(dev->hint_events_per_packet * EVDEV_BUF_PACKETS,
+                    EVDEV_MIN_BUFFER_SIZE);
+
+        return roundup_pow_of_two(n_events);
 }
 
 static int evdev_open(struct inode *inode, struct file *file)
diff --git a/include/linux/input.h b/include/linux/input.h
index 6fcc9101beeb..cc524c8b6703 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -1063,6 +1063,10 @@ struct ff_effect {
  * @sndbit: bitmap of sound effects supported by the device
  * @ffbit: bitmap of force feedback effects supported by the device
  * @swbit: bitmap of switches present on the device
+ * @hint_events_per_packet: average number of events generated by the
+ *      device in a packet (between EV_SYN/SYN_REPORT events). Used by
+ *      event handlers to estimate size of the buffer needed to hold
+ *      events.
  * @keycodemax: size of keycode table
  * @keycodesize: size of elements in keycode table
  * @keycode: map of scancodes to keycodes for this device
@@ -1140,6 +1144,8 @@ struct input_dev {
         unsigned long ffbit[BITS_TO_LONGS(FF_CNT)];
         unsigned long swbit[BITS_TO_LONGS(SW_CNT)];
 
+        unsigned int hint_events_per_packet;
+
         unsigned int keycodemax;
         unsigned int keycodesize;
         void *keycode;
@@ -1408,6 +1414,21 @@ static inline void input_mt_sync(struct input_dev *dev)
 
 void input_set_capability(struct input_dev *dev, unsigned int type, unsigned int code);
 
+/**
+ * input_set_events_per_packet - tell handlers about the driver event rate
+ * @dev: the input device used by the driver
+ * @n_events: the average number of events between calls to input_sync()
+ *
+ * If the event rate sent from a device is unusually large, use this
+ * function to set the expected event rate. This will allow handlers
+ * to set up an appropriate buffer size for the event stream, in order
+ * to minimize information loss.
+ */
+static inline void input_set_events_per_packet(struct input_dev *dev, int n_events)
+{
+        dev->hint_events_per_packet = n_events;
+}
+
 static inline void input_set_abs_params(struct input_dev *dev, int axis, int min, int max, int fuzz, int flat)
 {
         dev->absmin[axis] = min;