touchpad: correct a wrong slot count by the kernel

alps.c hardcodes 5 slots in the kernel but some devices only provide 2 slots
plus BTN_TOOL_TRIPLETAP, etc. Fix this by counting active slots and when the
fake finger count exceeds the active slots but is still less than the number
of slots, adjust the slots themselves downwards.

And because the new test device messes with our slot count assumptions for the
various tests hardcode that one device to return 2 slots.

Fixes #408

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

meson.build

@@ -770,6 +770,7 @@ if get_option('tests')
 		'test/litest-device-acer-hawaii-keyboard.c',
 		'test/litest-device-acer-hawaii-touchpad.c',
 		'test/litest-device-aiptek-tablet.c',
+		'test/litest-device-alps-3fg.c',
 		'test/litest-device-alps-semi-mt.c',
 		'test/litest-device-alps-dualpoint.c',
 		'test/litest-device-anker-mouse-kbd.c',

src/evdev-mt-touchpad.c

@@ -525,10 +525,14 @@ tp_process_absolute(struct tp_dispatch *tp,
 		tp->slot = e->value;
 		break;
 	case ABS_MT_TRACKING_ID:
-		if (e->value != -1)
+		if (e->value != -1) {
+			tp->nactive_slots += 1;
 			tp_new_touch(tp, t, time);
-		else
+		} else {
+			assert(tp->nactive_slots >= 1);
+			tp->nactive_slots -= 1;
 			tp_end_sequence(tp, t, time);
+		}
 		break;
 	case ABS_MT_PRESSURE:
 		t->pressure = e->value;
@@ -638,6 +642,32 @@ tp_process_fake_touches(struct tp_dispatch *tp,
 	    EVDEV_MODEL_SYNAPTICS_SERIAL_TOUCHPAD)
 		tp_restore_synaptics_touches(tp, time);
 
+	/* ALPS touchpads always set 3 slots in the kernel, even
+	 * where they support less than that. So we get BTN_TOOL_TRIPLETAP
+	 * but never slot 2 because our slot count is wrong.
+	 * This also means that the third touch falls through the cracks and
+	 * is ignored.
+	 *
+	 * All touchpad devices have at least one slot so we only do this
+	 * for 2 touches or higher.
+	 */
+	if (nfake_touches > 1 && tp->has_mt &&
+	    nfake_touches > tp->nactive_slots &&
+	    tp->nactive_slots < tp->num_slots) {
+		evdev_log_bug_kernel(tp->device,
+				     "Wrong slot count (%d), reducing to %d\n",
+				     tp->num_slots,
+				     tp->nactive_slots);
+		/* This should be safe since we fill the slots from the
+		 * first one so hiding the excessive slots shouldn't matter.
+		 * There are sequences where we could accidentally lose an
+		 * actual touch point but that requires specially crafted
+		 * sequences and let's deal with that when it happens.
+		 */
+		tp->num_slots = tp->nactive_slots;
+	}
+
+
 	start = tp->has_mt ? tp->num_slots : 0;
 	for (i = start; i < tp->ntouches; i++) {
 		t = tp_get_touch(tp, i);

src/evdev-mt-touchpad.h

@@ -268,6 +268,7 @@ struct tp_dispatch {
 		struct libinput_timer arbitration_timer;
 	} arbitration;
 
+	unsigned int nactive_slots;		/* number of active slots */
 	unsigned int num_slots;			/* number of slots */
 	unsigned int ntouches;			/* no slots inc. fakes */
 	struct tp_touch *touches;		/* len == ntouches */

test/litest-device-alps-3fg.c

@@ -0,0 +1,179 @@
+/*
+ * Copyright © 2020 Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <assert.h>
+
+#include "libinput-util.h"
+
+#include "litest.h"
+#include "litest-int.h"
+
+struct alps {
+	unsigned int first, second;
+	unsigned int active_touches;
+};
+
+static bool
+alps_create(struct litest_device *d)
+{
+	d->private = zalloc(sizeof(struct alps));
+	return true; /* we want litest to create our device */
+}
+
+static bool
+touch_down(struct litest_device *d, unsigned int slot, double x, double y)
+{
+	struct alps *alps = d->private;
+
+	alps->active_touches++;
+
+	if (alps->active_touches == 1)
+		alps->first = slot;
+	if (alps->active_touches == 2)
+		alps->second = slot;
+
+	/* This device announces 4 slots but only does two slots. So
+	 * anything over 2 slots we just drop for events,
+	 * litest takes care of BTN_TOOL_* for us. */
+	if (alps->active_touches > 2) {
+		/* Need to send SYN_REPORT to flush litest's BTN_TOOL_* updates */
+		litest_event(d, EV_SYN, SYN_REPORT,  0);
+		return true;
+	}
+
+	return false;
+}
+
+static bool
+touch_move(struct litest_device *d, unsigned int slot, double x, double y)
+{
+	struct alps *alps = d->private;
+
+	if (alps->active_touches > 2 &&
+	    slot != alps->first &&
+	    slot != alps->second)
+		return true;
+
+	return false;
+}
+
+static bool
+touch_up(struct litest_device *d, unsigned int slot)
+{
+	struct alps *alps = d->private;
+
+	assert(alps->active_touches >= 1);
+	alps->active_touches--;
+
+	/* Need to send SYN_REPORT to flush litest's BTN_TOOL_* updates */
+	if (alps->active_touches > 2 &&
+	    slot != alps->first &&
+	    slot != alps->second) {
+		litest_event(d, EV_SYN, SYN_REPORT,  0);
+		return true;
+	}
+
+	if (slot == alps->first)
+		alps->first = UINT_MAX;
+	if (slot == alps->second)
+		alps->second = UINT_MAX;
+
+	return false;
+}
+
+static struct input_event down[] = {
+	{ .type = EV_ABS, .code = ABS_X, .value = LITEST_AUTO_ASSIGN  },
+	{ .type = EV_ABS, .code = ABS_Y, .value = LITEST_AUTO_ASSIGN },
+	{ .type = EV_ABS, .code = ABS_MT_SLOT, .value = LITEST_AUTO_ASSIGN },
+	{ .type = EV_ABS, .code = ABS_MT_TRACKING_ID, .value = LITEST_AUTO_ASSIGN },
+	{ .type = EV_ABS, .code = ABS_MT_POSITION_X, .value = LITEST_AUTO_ASSIGN },
+	{ .type = EV_ABS, .code = ABS_MT_POSITION_Y, .value = LITEST_AUTO_ASSIGN },
+	{ .type = EV_SYN, .code = SYN_REPORT, .value = 0 },
+	{ .type = -1, .code = -1 },
+};
+
+static struct input_event move[] = {
+	{ .type = EV_ABS, .code = ABS_MT_SLOT, .value = LITEST_AUTO_ASSIGN },
+	{ .type = EV_ABS, .code = ABS_X, .value = LITEST_AUTO_ASSIGN  },
+	{ .type = EV_ABS, .code = ABS_Y, .value = LITEST_AUTO_ASSIGN },
+	{ .type = EV_ABS, .code = ABS_MT_POSITION_X, .value = LITEST_AUTO_ASSIGN },
+	{ .type = EV_ABS, .code = ABS_MT_POSITION_Y, .value = LITEST_AUTO_ASSIGN },
+	{ .type = EV_SYN, .code = SYN_REPORT, .value = 0 },
+	{ .type = -1, .code = -1 },
+};
+
+static struct litest_device_interface interface = {
+	.touch_down_events = down,
+	.touch_move_events = move,
+
+	.touch_down = touch_down,
+	.touch_move = touch_move,
+	.touch_up = touch_up,
+};
+
+static struct input_id input_id = {
+	.bustype = 0x11,
+	.vendor = 0x2,
+	.product = 0x8,
+	.version = 0x700,
+};
+
+static int events[] = {
+	EV_KEY, BTN_LEFT,
+	EV_KEY, BTN_RIGHT,
+	EV_KEY, BTN_MIDDLE,
+	EV_KEY, BTN_TOOL_FINGER,
+	EV_KEY, BTN_TOUCH,
+	EV_KEY, BTN_TOOL_DOUBLETAP,
+	EV_KEY, BTN_TOOL_TRIPLETAP,
+	EV_KEY, BTN_TOOL_QUADTAP,
+	EV_KEY, BTN_TOOL_QUINTTAP,
+	INPUT_PROP_MAX, INPUT_PROP_POINTER,
+	-1, -1,
+};
+
+/* Note: we use the user-supplied resolution here, see #408 */
+static struct input_absinfo absinfo[] = {
+	{ ABS_X, 0, 4095, 0, 0, 37 },
+	{ ABS_Y, 0, 2047, 0, 0, 26 },
+	{ ABS_PRESSURE, 0, 127, 0, 0, 0 },
+	{ ABS_MT_SLOT, 0, 3, 0, 0, 0 },
+	{ ABS_MT_POSITION_X, 0, 4095, 0, 0, 37 },
+	{ ABS_MT_POSITION_Y, 0, 2047, 0, 0, 26 },
+	{ ABS_MT_TRACKING_ID, 0, 65535, 0, 0, 0 },
+	{ .value = -1 }
+};
+
+TEST_DEVICE("alps-3fg",
+	.type = LITEST_ALPS_3FG,
+	.features = LITEST_TOUCHPAD | LITEST_BUTTON,
+	.interface = &interface,
+
+	.name = "AlpsPS/2 ALPS GlidePoint",
+	.id = &input_id,
+	.events = events,
+	.absinfo = absinfo,
+	.create = alps_create,
+)

test/litest.h

@@ -300,6 +300,7 @@ enum litest_device_type {
 	LITEST_DELL_CANVAS_TOTEM,
 	LITEST_DELL_CANVAS_TOTEM_TOUCH,
 	LITEST_WACOM_ISDV4_4200_PEN,
+	LITEST_ALPS_3FG,
 };
 
 #define LITEST_DEVICELESS	-2
@@ -1151,6 +1152,9 @@ litest_send_file(int sock, int fd)
 
 static inline int litest_slot_count(struct litest_device *dev)
 {
+	if (dev->which == LITEST_ALPS_3FG)
+		return 2;
+
 	return libevdev_get_num_slots(dev->evdev);
 }