[PATCH 3/3] input: use driver hint to compute the evdev buffer size

["Henrik Rydberg" <rydberg@euromail.se>]

Some devices, in particular MT devices, produce a lot of data.
This leads to a high frequency of lost packets in evdev, which
by default uses a fairly small event buffer. Let the drivers hint
the average number of events per packet for the device by calling
the input_set_events_per_packet(), and use that information when
computing the evdev buffer size.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
---
 drivers/input/evdev.c |    5 ++++-
 include/linux/input.h |    7 +++++++
 2 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 327f821..fdddb43 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -11,6 +11,7 @@
 #define EVDEV_MINOR_BASE	64
 #define EVDEV_MINORS		32
 #define EVDEV_MIN_BUFFER_SIZE	64
+#define EVDEV_BUF_PACKETS	8
 
 #include <linux/poll.h>
 #include <linux/sched.h>
@@ -807,7 +808,9 @@ static void evdev_cleanup(struct evdev *evdev)
 
 static int evdev_compute_buffer_size(struct input_dev *dev)
 {
-	return EVDEV_MIN_BUFFER_SIZE;
+	int nev = dev->hint_events_per_packet * EVDEV_BUF_PACKETS;
+	nev = max(nev, EVDEV_MIN_BUFFER_SIZE);
+	return roundup_pow_of_two(nev);
 }
 
 /*
diff --git a/include/linux/input.h b/include/linux/input.h
index bd00786..35b015d 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -1162,6 +1162,8 @@ 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;
@@ -1439,6 +1441,11 @@ static inline void input_mt_slot(struct input_dev *dev, int slot)
 
 void input_set_capability(struct input_dev *dev, unsigned int type, unsigned int code);
 
+static inline void input_set_events_per_packet(struct input_dev *dev, int nev)
+{
+	dev->hint_events_per_packet = nev;
+}
+
 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;
-- 
1.6.3.3