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Subject[PATCH 2.6] Mousedev - better button handling under load
Date
Hi,

Currently mousedev combines all hardware motion data that arrivers since
last time userspace read data into one cooked PS/2 packet. The problem is
that under heavy or even moderate load, when userspace can't read data
quickly enough, we start loosing valuable data which manifests in:

- ignoring buton presses as by the time userspace gets to read the data
button has already been released;
- click starts in wrong place - by the time userspace got aroungd and read
the packet mouse moved half way across the screen.

The patch below corrects the issue - it will start accumulating new packet
every time userspace is behind and button set changes. Size of the buffer
is 16 packets, i.e. up to 8 pairs of press/release events which should be
more than enough.

The patch is against Vojtech's tree and shuld apply to -mm. I also have
cumulative mousedev patch done against 2.6.7-pre2 at:

http://www.geocities.com/dt_or/input/misc/mousedev-2.6.7-rc2-cumulative.patch.gz

--
Dmitry


===================================================================

ChangeSet@1.1828, 2004-06-05 01:05:50-05:00, dtor_core@ameritech.net
Input: mousedev - better handle button presses when under load

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>


mousedev.c | 152 +++++++++++++++++++++++++++++++++++++++++--------------------
1 files changed, 104 insertions(+), 48 deletions(-)

===================================================================


diff -Nru a/drivers/input/mousedev.c b/drivers/input/mousedev.c
--- a/drivers/input/mousedev.c 2004-06-05 02:08:31 -05:00
+++ b/drivers/input/mousedev.c 2004-06-05 02:08:31 -05:00
@@ -50,6 +50,7 @@

struct mousedev_motion {
int dx, dy, dz;
+ unsigned long buttons;
};

struct mousedev {
@@ -62,21 +63,31 @@
struct input_handle handle;

struct mousedev_motion packet;
- unsigned long buttons;
unsigned int pkt_count;
int old_x[4], old_y[4];
unsigned int touch;
};

+enum mousedev_emul {
+ MOUSEDEV_EMUL_PS2,
+ MOUSEDEV_EMUL_IMPS,
+ MOUSEDEV_EMUL_EXPS
+} __attribute__ ((packed));
+
+#define PACKET_QUEUE_LEN 16
struct mousedev_list {
struct fasync_struct *fasync;
struct mousedev *mousedev;
struct list_head node;
- int dx, dy, dz;
- unsigned long buttons;
+
+ struct mousedev_motion packets[PACKET_QUEUE_LEN];
+ unsigned int head, tail;
+ spinlock_t packet_lock;
+
signed char ps2[6];
unsigned char ready, buffer, bufsiz;
- unsigned char mode, imexseq, impsseq;
+ unsigned char imexseq, impsseq;
+ enum mousedev_emul mode;
};

#define MOUSEDEV_SEQ_LEN 6
@@ -165,24 +176,40 @@
}

if (value) {
- set_bit(index, &mousedev->buttons);
- set_bit(index, &mousedev_mix.buttons);
+ set_bit(index, &mousedev->packet.buttons);
+ set_bit(index, &mousedev_mix.packet.buttons);
} else {
- clear_bit(index, &mousedev->buttons);
- clear_bit(index, &mousedev_mix.buttons);
+ clear_bit(index, &mousedev->packet.buttons);
+ clear_bit(index, &mousedev_mix.packet.buttons);
}
}

static void mousedev_notify_readers(struct mousedev *mousedev, struct mousedev_motion *packet)
{
struct mousedev_list *list;
+ struct mousedev_motion *p;
+ unsigned long flags;

list_for_each_entry(list, &mousedev->list, node) {
- list->dx += packet->dx;
- list->dy += packet->dy;
- list->dz += packet->dz;
- list->buttons = mousedev->buttons;
+ spin_lock_irqsave(&list->packet_lock, flags);
+
+ p = &list->packets[list->head];
+ if (list->ready && p->buttons != packet->buttons) {
+ unsigned int new_head = (list->head + 1) % PACKET_QUEUE_LEN;
+ if (new_head != list->tail) {
+ p = &list->packets[list->head = new_head];
+ memset(p, 0, sizeof(struct mousedev_motion));
+ }
+ }
+
+ p->dx += packet->dx;
+ p->dy += packet->dy;
+ p->dz += packet->dz;
+ p->buttons = mousedev->packet.buttons;
+
list->ready = 1;
+
+ spin_unlock_irqrestore(&list->packet_lock, flags);
kill_fasync(&list->fasync, SIGIO, POLL_IN);
}

@@ -237,7 +264,7 @@
mousedev_notify_readers(mousedev, &mousedev->packet);
mousedev_notify_readers(&mousedev_mix, &mousedev->packet);

- memset(&mousedev->packet, 0, sizeof(struct mousedev_motion));
+ mousedev->packet.dx = mousedev->packet.dy = mousedev->packet.dz = 0;
}
break;
}
@@ -322,6 +349,7 @@
return -ENOMEM;
memset(list, 0, sizeof(struct mousedev_list));

+ spin_lock_init(&list->packet_lock);
list->mousedev = mousedev_table[i];
list_add_tail(&list->node, &mousedev_table[i]->list);
file->private_data = list;
@@ -341,32 +369,56 @@
return 0;
}

-static void mousedev_packet(struct mousedev_list *list, unsigned char off)
+static inline int mousedev_limit_delta(int delta, int limit)
{
- list->ps2[off] = 0x08 | ((list->dx < 0) << 4) | ((list->dy < 0) << 5) | (list->buttons & 0x07);
- list->ps2[off + 1] = (list->dx > 127 ? 127 : (list->dx < -127 ? -127 : list->dx));
- list->ps2[off + 2] = (list->dy > 127 ? 127 : (list->dy < -127 ? -127 : list->dy));
- list->dx -= list->ps2[off + 1];
- list->dy -= list->ps2[off + 2];
- list->bufsiz = off + 3;
-
- if (list->mode == 2) {
- list->ps2[off + 3] = (list->dz > 7 ? 7 : (list->dz < -7 ? -7 : list->dz));
- list->dz -= list->ps2[off + 3];
- list->ps2[off + 3] = (list->ps2[off + 3] & 0x0f) | ((list->buttons & 0x18) << 1);
- list->bufsiz++;
- } else {
- list->ps2[off] |= ((list->buttons & 0x10) >> 3) | ((list->buttons & 0x08) >> 1);
+ return delta > limit ? limit : (delta < -limit ? -limit : delta);
+}
+
+static void mousedev_packet(struct mousedev_list *list, signed char *ps2_data)
+{
+ struct mousedev_motion *p;
+ unsigned long flags;
+
+ spin_lock_irqsave(&list->packet_lock, flags);
+ p = &list->packets[list->tail];
+
+ ps2_data[0] = 0x08 | ((p->dx < 0) << 4) | ((p->dy < 0) << 5) | (p->buttons & 0x07);
+ ps2_data[1] = mousedev_limit_delta(p->dx, 127);
+ ps2_data[2] = mousedev_limit_delta(p->dy, 127);
+ p->dx -= ps2_data[1];
+ p->dy -= ps2_data[2];
+
+ switch (list->mode) {
+ case MOUSEDEV_EMUL_EXPS:
+ ps2_data[3] = mousedev_limit_delta(p->dz, 127);
+ p->dz -= ps2_data[3];
+ ps2_data[3] = (ps2_data[3] & 0x0f) | ((p->buttons & 0x18) << 1);
+ list->bufsiz = 4;
+ break;
+
+ case MOUSEDEV_EMUL_IMPS:
+ ps2_data[0] |= ((p->buttons & 0x10) >> 3) | ((p->buttons & 0x08) >> 1);
+ ps2_data[3] = mousedev_limit_delta(p->dz, 127);
+ p->dz -= ps2_data[3];
+ list->bufsiz = 4;
+ break;
+
+ case MOUSEDEV_EMUL_PS2:
+ default:
+ ps2_data[0] |= ((p->buttons & 0x10) >> 3) | ((p->buttons & 0x08) >> 1);
+ p->dz = 0;
+ list->bufsiz = 3;
+ break;
}

- if (list->mode == 1) {
- list->ps2[off + 3] = (list->dz > 127 ? 127 : (list->dz < -127 ? -127 : list->dz));
- list->dz -= list->ps2[off + 3];
- list->bufsiz++;
+ if (!p->dx && !p->dy && !p->dz) {
+ if (list->tail != list->head)
+ list->tail = (list->tail + 1) % PACKET_QUEUE_LEN;
+ if (list->tail == list->head)
+ list->ready = 0;
}

- if (!list->dx && !list->dy && (!list->mode || !list->dz)) list->ready = 0;
- list->buffer = list->bufsiz;
+ spin_unlock_irqrestore(&list->packet_lock, flags);
}


@@ -384,31 +436,31 @@
if (c == mousedev_imex_seq[list->imexseq]) {
if (++list->imexseq == MOUSEDEV_SEQ_LEN) {
list->imexseq = 0;
- list->mode = 2;
+ list->mode = MOUSEDEV_EMUL_EXPS;
}
} else list->imexseq = 0;

if (c == mousedev_imps_seq[list->impsseq]) {
if (++list->impsseq == MOUSEDEV_SEQ_LEN) {
list->impsseq = 0;
- list->mode = 1;
+ list->mode = MOUSEDEV_EMUL_IMPS;
}
} else list->impsseq = 0;

list->ps2[0] = 0xfa;
- list->bufsiz = 1;

switch (c) {

case 0xeb: /* Poll */
- mousedev_packet(list, 1);
+ mousedev_packet(list, &list->ps2[1]);
+ list->bufsiz++; /* account for leading ACK */
break;

case 0xf2: /* Get ID */
switch (list->mode) {
- case 0: list->ps2[1] = 0; break;
- case 1: list->ps2[1] = 3; break;
- case 2: list->ps2[1] = 4; break;
+ case MOUSEDEV_EMUL_PS2: list->ps2[1] = 0; break;
+ case MOUSEDEV_EMUL_IMPS: list->ps2[1] = 3; break;
+ case MOUSEDEV_EMUL_EXPS: list->ps2[1] = 4; break;
}
list->bufsiz = 2;
break;
@@ -419,13 +471,15 @@
break;

case 0xff: /* Reset */
- list->impsseq = 0;
- list->imexseq = 0;
- list->mode = 0;
- list->ps2[1] = 0xaa;
- list->ps2[2] = 0x00;
+ list->impsseq = list->imexseq = 0;
+ list->mode = MOUSEDEV_EMUL_PS2;
+ list->ps2[1] = 0xaa; list->ps2[2] = 0x00;
list->bufsiz = 3;
break;
+
+ default:
+ list->bufsiz = 1;
+ break;
}

list->buffer = list->bufsiz;
@@ -451,8 +505,10 @@
if (retval)
return retval;

- if (!list->buffer && list->ready)
- mousedev_packet(list, 0);
+ if (!list->buffer && list->ready) {
+ mousedev_packet(list, list->ps2);
+ list->buffer = list->bufsiz;
+ }

if (count > list->buffer)
count = list->buffer;
-
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