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 | 17 +++++++++++++++++
2 files changed, 21 insertions(+), 1 deletions(-)

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index 463bf1b..2cf7b3a 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>
@@ -797,7 +798,9 @@ 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 20e4eac..9e024b6 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 +1441,21 @@ 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);

+/**
+ * input_set_events_per_packet - tell handlers about the driver event rate
+ * @dev: the input device used by the driver
+ * @nev: 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 approriate 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 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


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