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    Subject[PATCH 4/4] input: Use driver hint to compute the evdev buffer size
    Date
    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 2e2a339..f08b1d2 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>
    @@ -790,7 +791,9 @@ 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


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