[RFC v3] Add ff-memless-next

["Michal Malý" <madcatxster@prifuk.cz>]

One case where uncombinable effects were mishandled was corrected. Rest of
the changes are just coding style fixes.

Tested-by: Elias Vanderstuyft <elias.vds@gmail.com>
Signed-off-by: Michal Malý <madcatxster@prifuk.cz>
---
>From 2de27604adeefa73e30ee049fae4c38265beb85d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michal=20Mal=C3=BD?= <madcatxster@prifuk.cz>
Date: Mon, 23 Dec 2013 23:42:11 +0100
Subject: [PATCH] Add ff-memless-next

---
 Documentation/input/ff-memless-next.txt | 145 ++++++
 drivers/input/Kconfig                   |  12 +
 drivers/input/Makefile                  |   2 +
 drivers/input/ff-memless-next.c         | 786 ++++++++++++++++++++++++++++++++
 include/linux/input/ff-memless-next.h   |  31 ++
 5 files changed, 976 insertions(+)
 create mode 100644 Documentation/input/ff-memless-next.txt
 create mode 100644 drivers/input/ff-memless-next.c
 create mode 100644 include/linux/input/ff-memless-next.h

diff --git a/Documentation/input/ff-memless-next.txt b/Documentation/input/ff-memless-next.txt
new file mode 100644
index 0000000..00f893d
--- /dev/null
+++ b/Documentation/input/ff-memless-next.txt
@@ -0,0 +1,145 @@
+"ff-memless-next" force feedback module for memoryless devices.
+By Michal Malý <madcatxster@prifuk.cz> on 2013/12/21
+----------------------------------------------------------------------------
+
+1. Introduction
+~~~~~~~~~~~~~~~
+This document describes basic working principles of the "ff-memless-next"
+and its purpose. This document also contains summary of "ff-memless-next" API
+and brief instructions on how to use it to write a hardware-specific backend
+with "ff-memless-next". Some specifics of ff-memless-next that might be of
+interest for userspace developers are also discussed.
+
+2. Basic principles of ff-memless-next
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+A lot of commonly used force feedback devices do not have a memory of their
+own. This means that it is not possible to upload a force feedback effect
+to such a device and let the device's CPU handle the playback. Instead,
+the device relies solely on its driver to tell it what force to generate.
+"ff-memless-next" was written to serve in this capacity. Its purpose is to
+calculate the overall force the device should apply and pass the result to
+a hardware-specific backend which then submits the appropriate command to
+the device.
+
+"ff-memless-next" differentiates between two types of force feedback effects,
+"combinable" and "uncombinable".
+"Combinable" effects are effects that generate a force of a given
+magnitude and direction. The magnitude can change in time according to the
+envelope of the effect and its waveform; the latter applies only to periodic
+effects. Force generated by "combinable" effect does not depend on the position
+of the device. Forces generated by each "combinable" effect that is active
+are periodically recalculated as needed and superposed into one overall force.
+"Combinable" effects are FF_CONSTANT, FF_PERIODIC and FF_RAMP.
+
+"Uncombinable" effects generate a force that depends on the position of
+the device. "ff-memless-next" assumes that the device takes care of processing
+such an effect. However, a device might have a limit on how many "uncombinable"
+effects can be active at once and this limit might be lower than the maximum
+effect count set in "ff-memless-next". "ff-memless-next" allows a
+hardware-specific driver to check whether the device is able to play
+an "uncombinable" effect. Error is reported back to userspace if the device
+cannot play the effect. The hardware-specific driver may choose not to
+perform this check in which case the userspace will have no way of knowing
+whether an "uncombinable" is really being played or not.
+
+3. API provided by "ff-memless-next"
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+"ff-memless-next" provides an API for developers of hardware-specific
+drivers. In order to use the API, the hardware-specific driver should
+include <linux/input/ff-memless-next.h>
+Functions and structs defined by this API are:
+
+int input_ff_create_mlnx(struct input_dev *dev, void *data,
+			 int(*control_effect)(struct input_dev *, void *, const struct mlnx_effect_command *),
+			 const u16 update_rate)
+- Any hardware-specific driver that wants to use "ff-memless-next" must call
+this function. The function takes care of creating and registering a force
+feedback device within the kernel. It also initializes resources needed by
+"ff-memless-next" to handle a new device. No other initialization steps are necessary.
+	Parameters:
+	* dev - pointer to valid struct input_dev
+	* data - pointer to custom data the hardware-specific backend
+		 might need to pass to the control_effect() callback function
+		 (discussed later). * data will be freed automatically by
+		 "ff-memless-next" upon device's destruction.
+	* control_effect - A callback function. "ff-memless-next" will call
+			   this function when it is done processing effects.
+			   Implementation of control_effect() in the
+			   hardware-specific driver should create an appropriate
+			   command and submit it to the device.
+			   This function is called with dev->event_lock
+			   spinlock held.
+	update_rate - Rate in milliseconds at which envelopes and periodic
+		      effects are recalculated. Minimum value is limited by the
+		      kernel timer resolution and changes with value of
+		      CONFIG_HZ.
+
+struct mlnx_effect_command
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+- This struct is passed to the hardware-specific backend in
+the control_effect() function. See "ff-memless-next.h" for details.
+
+enum mlnx_commands
+^^^^^^^^^^^^^^^^^^
+- Types of commands generated by ff-memless-next
+	MLNX_START_COMBINED - Start or update "combinable" effect
+	MLNX_STOP_COMBINED - Stop "combinable" effect. In most cases this means
+			     to set the force to zero.
+	MLNX_UPLOAD_UNCOMB - Check if the device can accept and play
+			     "uncombinable" effect.
+			     Hardware-specific driver should return 0
+			     on success.
+	MLNX_START_UNCOMB - Start playback of "uncombinable" effect.
+	MLNX_STOP_UNCOMB - Stop playback of "uncombinable" effect.
+
+struct mlnx_simple_force
+^^^^^^^^^^^^^^^^^^^^^^^^
+	x - overall force along X axis
+	y - overall force along Y axis
+
+struct mlnx_uncomb_effect
+^^^^^^^^^^^^^^^^^^^^^^^^^
+- Information about "uncombinable" effect.
+	id - internal ID of the effect
+	* effect - pointer to the internal copy of the effect kept by
+		   "ff-memless-next". This pointer will remain valid until
+		   the effect is removed.
+
+Sample implementation of a dummy driver that uses "ff-memless-next" is
+available at "git://prifuk.cz/ff-dummy-device". Link to the source will
+be kept up to date.
+
+Direction of the effect's force translates to Cartesian coordinates system
+as follows:
+  Direction = 0: Down
+  Direction (0; 16384): 3rd quadrant
+  Direction = 16384: Left
+  Direction (16385; 32768): 2nd quadrant
+  Direction = 32768: Up
+  Direction (32769; 49152): 1st quadrant
+  Direction = 49152: Right
+  Direction (49153; 65535) :4th quadrant
+  Direction = 65565: Down
+
+4. Specifics of "ff-memless-next" for userspace developers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+None of the persons involved in development or testing of "ff-memless-next"
+is aware of any reference force feedback specifications. "ff-memless-next"
+tries to adhere to Microsoft's DirectInput specifications because we
+believe that is what most developers have experience with.
+
+- Waveforms of periodic effects do not start at the origin, but as follows:
+	SAW_UP: At minimum
+	SAW_DOWN: At maximum
+	SQUARE: At maximum
+	TRIANGLE: At maximum
+	SINE: At origin
+
+- Updating periodic effects:
+	- All periodic effects are restarted when their parameters are updated.
+
+- Updating effects of finite duration:
+	- Once an effect of finite length finishes playing, it is considered
+	  stopped. Only effects that are playing can be updated on the fly.
+	  Therefore effects of finite duration can by updated only until
+	  they finish playing.
diff --git a/drivers/input/Kconfig b/drivers/input/Kconfig
index a11ff74..893ab00 100644
--- a/drivers/input/Kconfig
+++ b/drivers/input/Kconfig
@@ -77,6 +77,18 @@ config INPUT_MATRIXKMAP
 	  To compile this driver as a module, choose M here: the
 	  module will be called matrix-keymap.
 
+config INPUT_FF_MEMLESS_NEXT
+	tristate "New version of support for memoryless force feedback devices"
+	help
+	  Say Y here if you want to enable support for various memoryless
+	  force feedback devices (as of now there is no hardware-specific
+	  driver that supports this)
+
+	  If unsure, say N.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ff-memless-next.
+
 comment "Userland interfaces"
 
 config INPUT_MOUSEDEV
diff --git a/drivers/input/Makefile b/drivers/input/Makefile
index 5ca3f63..269a22d 100644
--- a/drivers/input/Makefile
+++ b/drivers/input/Makefile
@@ -16,6 +16,8 @@ obj-$(CONFIG_INPUT_MOUSEDEV)	+= mousedev.o
 obj-$(CONFIG_INPUT_JOYDEV)	+= joydev.o
 obj-$(CONFIG_INPUT_EVDEV)	+= evdev.o
 obj-$(CONFIG_INPUT_EVBUG)	+= evbug.o
+obj-$(CONFIG_INPUT_MATRIXKMAP)	+= matrix-keymap.o
+obj-$(CONFIG_INPUT_FF_MEMLESS_NEXT)	+= ff-memless-next.o
 
 obj-$(CONFIG_INPUT_KEYBOARD)	+= keyboard/
 obj-$(CONFIG_INPUT_MOUSE)	+= mouse/
diff --git a/drivers/input/ff-memless-next.c b/drivers/input/ff-memless-next.c
new file mode 100644
index 0000000..979b823
--- /dev/null
+++ b/drivers/input/ff-memless-next.c
@@ -0,0 +1,786 @@
+/*
+ * Force feedback support for memoryless devices
+ *
+ * This module is based on "ff-memless" orignally written by Anssi Hannula.
+ * It is extended to support all force feedback effects currently supported
+ * by the Linux input stack.
+ *
+ * Copyright(c) 2013 Michal Maly <madcatxster@prifuk.cz>
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+#include <linux/jiffies.h>
+#include <linux/fixp-arith.h>
+#include <linux/input/ff-memless-next.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Michal \"MadCatX\" Maly");
+MODULE_DESCRIPTION("Force feedback support for memoryless force feedback devices");
+
+#define FF_MAX_EFFECTS 16
+#define FF_MIN_EFFECT_LENGTH ((1000 / CONFIG_HZ) + 1)
+#define FF_EFFECT_STARTED 1
+#define FF_EFFECT_PLAYING 2
+
+
+struct mlnx_effect {
+	struct ff_effect effect;
+	unsigned long flags;
+	unsigned long begin_at;
+	unsigned long stop_at;
+	unsigned long updated_at;
+	unsigned long attack_stop;
+	unsigned long fade_begin;
+	int repeat;
+	u16 playback_time;
+};
+
+struct mlnx_device {
+	u8 combinable_playing;
+	unsigned long update_rate_jiffies;
+	void *private;
+	struct mlnx_effect effects[FF_MAX_EFFECTS];
+	int gain;
+	struct timer_list timer;
+	struct input_dev *dev;
+
+	int (*control_effect)(struct input_dev *, void *,
+			      const struct mlnx_effect_command *);
+};
+
+static __always_inline s32 mlnx_calculate_x_force(const s32 level,
+						  const u16 direction)
+{
+	s32 new = (level * -fixp_sin(direction)) >> FRAC_N;
+	pr_debug("x force: %d\n", new);
+	return new;
+}
+
+static __always_inline s32 mlnx_calculate_y_force(const s32 level,
+						  const u16 direction)
+{
+	s32 new = (level * -fixp_cos(direction)) >> FRAC_N;
+	pr_debug("y force: %d\n", new);
+	return new;
+}
+
+static inline bool mlnx_is_combinable(const struct ff_effect *effect)
+{
+	switch (effect->type) {
+	case FF_CONSTANT:
+	case FF_PERIODIC:
+	case FF_RAMP:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static inline bool mlnx_is_conditional(const struct ff_effect *effect)
+{
+	switch (effect->type) {
+	case FF_DAMPER:
+	case FF_FRICTION:
+	case FF_INERTIA:
+	case FF_SPRING:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static __always_inline bool mlnx_is_square(const struct ff_effect *effect)
+{
+	if (effect->type == FF_PERIODIC)
+		return effect->u.periodic.waveform == FF_SQUARE;
+	return false;
+}
+
+static __always_inline void mlnx_clr_playing(struct mlnx_effect *mlnxeff)
+{
+	__clear_bit(FF_EFFECT_PLAYING, &mlnxeff->flags);
+}
+
+static __always_inline void mlnx_clr_started(struct mlnx_effect *mlnxeff)
+{
+	__clear_bit(FF_EFFECT_STARTED, &mlnxeff->flags);
+}
+
+static __always_inline bool mlnx_is_playing(const struct mlnx_effect *mlnxeff)
+{
+	return test_bit(FF_EFFECT_PLAYING, &mlnxeff->flags);
+}
+
+static __always_inline bool mlnx_is_started(const struct mlnx_effect *mlnxeff)
+{
+	return test_bit(FF_EFFECT_STARTED, &mlnxeff->flags);
+}
+
+static __always_inline bool mlnx_test_set_playing(struct mlnx_effect *mlnxeff)
+{
+	return test_and_set_bit(FF_EFFECT_PLAYING, &mlnxeff->flags);
+}
+
+static const struct ff_envelope *mlnx_get_envelope(const struct ff_effect *effect)
+{
+	static const struct ff_envelope empty;
+
+	switch (effect->type) {
+	case FF_CONSTANT:
+		return &effect->u.constant.envelope;
+	case FF_PERIODIC:
+		return &effect->u.periodic.envelope;
+	case FF_RAMP:
+		return &effect->u.ramp.envelope;
+	default:
+		return &empty;
+	}
+}
+
+/* Some devices might have a limit on how many uncombinable effects
+ * can be played at once */
+static int mlnx_upload_conditional(struct mlnx_device *mlnxdev,
+				   const struct ff_effect *effect)
+{
+	struct mlnx_effect_command ecmd = { .cmd = MLNX_UPLOAD_UNCOMB,
+					    .u.uncomb.id = effect->id,
+					    .u.uncomb.effect = effect };
+	return mlnxdev->control_effect(mlnxdev->dev, mlnxdev->private, &ecmd);
+}
+
+static void mlnx_set_envelope_times(struct mlnx_effect *mlnxeff)
+{
+	const struct ff_effect *effect = &mlnxeff->effect;
+	const struct ff_envelope *envelope = mlnx_get_envelope(effect);
+
+	if (envelope->attack_length) {
+		unsigned long j = msecs_to_jiffies(envelope->attack_length);
+		mlnxeff->attack_stop = mlnxeff->begin_at + j;
+	}
+	if (effect->replay.length && envelope->fade_length) {
+		unsigned long j = msecs_to_jiffies(envelope->fade_length);
+		mlnxeff->fade_begin = mlnxeff->stop_at - j;
+	}
+}
+
+static void mlnx_set_trip_times(struct mlnx_effect *mlnxeff,
+				const unsigned long now)
+{
+	const struct ff_effect *effect = &mlnxeff->effect;
+	const u16 replay_delay = effect->replay.delay;
+	const u16 replay_length = effect->replay.length;
+
+	mlnxeff->begin_at = now + msecs_to_jiffies(replay_delay);
+	mlnxeff->stop_at = mlnxeff->begin_at + msecs_to_jiffies(replay_length);
+	mlnxeff->updated_at = mlnxeff->begin_at;
+	if (effect->type == FF_PERIODIC)
+		mlnxeff->playback_time = effect->u.periodic.phase;
+}
+
+static void mlnx_start_effect(struct mlnx_effect *mlnxeff)
+{
+	const unsigned long now = jiffies;
+
+	mlnx_set_trip_times(mlnxeff, now);
+	mlnx_set_envelope_times(mlnxeff);
+	__set_bit(FF_EFFECT_STARTED, &mlnxeff->flags);
+}
+
+static void mlnx_stop_effect(struct mlnx_device *mlnxdev,
+			     const struct mlnx_effect *mlnxeff)
+{
+	switch (mlnxeff->effect.type) {
+	case FF_CONSTANT:
+	case FF_PERIODIC:
+	case FF_RAMP:
+		if (--mlnxdev->combinable_playing == 0) {
+			const struct mlnx_effect_command c = { .cmd = MLNX_STOP_COMBINED };
+			mlnxdev->control_effect(mlnxdev->dev, mlnxdev->private,
+						&c);
+		}
+		return;
+	case FF_DAMPER:
+	case FF_FRICTION:
+	case FF_INERTIA:
+	case FF_SPRING:
+	{
+		const struct mlnx_effect_command c = { .cmd = MLNX_STOP_UNCOMB,
+						       .u.uncomb.id = mlnxeff->effect.id,
+						       .u.uncomb.effect = &mlnxeff->effect };
+		mlnxdev->control_effect(mlnxdev->dev, mlnxdev->private, &c);
+		return;
+	}
+	default:
+		return;
+	}
+}
+
+static int mlnx_restart_effect(struct mlnx_device *mlnxdev,
+			       struct mlnx_effect *mlnxeff)
+{
+	const struct ff_effect *effect = &mlnxeff->effect;
+	const unsigned long now = jiffies;
+
+	if (mlnx_is_combinable(effect)) {
+		if (effect->replay.delay)
+			mlnx_stop_effect(mlnxdev, mlnxeff);
+		else
+			mlnxdev->combinable_playing--;
+	} else if (mlnx_is_conditional(effect)) {
+		int ret;
+		if (effect->replay.delay)
+			mlnx_stop_effect(mlnxdev, mlnxeff);
+
+		ret = mlnx_upload_conditional(mlnxdev, &mlnxeff->effect);
+		if (ret)
+			return ret;
+	}
+
+	mlnx_set_trip_times(mlnxeff, now);
+	mlnx_set_envelope_times(mlnxeff);
+
+	return 0;
+}
+
+static s32 mlnx_apply_envelope(const struct mlnx_effect *mlnxeff,
+			       const s32 level)
+{
+	const struct ff_effect *effect = &mlnxeff->effect;
+	const struct ff_envelope *envelope = mlnx_get_envelope(effect);
+	const unsigned long now = jiffies;
+	const s32 alevel = abs(level);
+
+	/* Effect has an envelope with nonzero attack time */
+	if (envelope->attack_length && time_before(now, mlnxeff->attack_stop)) {
+		const s32 clength = jiffies_to_msecs(now - mlnxeff->begin_at);
+		const s32 alength = envelope->attack_length;
+		const s32 dlevel = (alevel - envelope->attack_level)
+				 * clength / alength;
+		return level < 0 ? -(dlevel + envelope->attack_level) :
+				    (dlevel + envelope->attack_level);
+	} else if (envelope->fade_length && time_before_eq(mlnxeff->fade_begin, now)) {
+		const s32 clength = jiffies_to_msecs(now - mlnxeff->fade_begin);
+		const s32 flength = envelope->fade_length;
+		const s32 dlevel = (envelope->fade_level - alevel)
+				 * clength / flength;
+		return level < 0 ? -(dlevel + alevel) : (dlevel + alevel);
+	}
+
+	return level;
+}
+
+static s32 mlnx_calculate_periodic(struct mlnx_effect *mlnxeff, const s32 level)
+{
+	const struct ff_effect *effect = &mlnxeff->effect;
+	const unsigned long now = jiffies;
+	const u16 period = effect->u.periodic.period;
+	const unsigned long dt = jiffies_to_msecs(now - mlnxeff->updated_at);
+	const s16 offset = effect->u.periodic.offset;
+	s32 new = level;
+	u16 t;
+
+	mlnxeff->playback_time += dt;
+	t = mlnxeff->playback_time % period;
+
+	switch (effect->u.periodic.waveform) {
+	case FF_SINE:
+	{
+		u16 degrees = (360 * t) / period;
+		new = ((level * fixp_sin(degrees)) >> FRAC_N) + offset;
+		break;
+	}
+	case FF_SQUARE:
+	{
+		u16 degrees = (360 * t) / period;
+		new = level * (degrees < 180 ? 1 : -1) + offset;
+		break;
+	}
+	case FF_SAW_UP:
+		new = 2 * level * t / period - level + offset;
+		break;
+	case FF_SAW_DOWN:
+		new = level - 2 * level * t / period + offset;
+		break;
+	case FF_TRIANGLE:
+	{
+		new = (2 * abs(level - (2 * level * t) / period));
+		new = new - level + offset;
+		break;
+	}
+	case FF_CUSTOM:
+		pr_debug("Custom waveform is not handled by this driver.\n");
+		return level;
+	default:
+		pr_err("Invalid waveform.\n");
+		return level;
+	}
+
+	mlnxeff->playback_time = t;
+	/* Ensure that the offset did not make the value exceed s16 range */
+	new = clamp(new, -0x7fff, 0x7fff);
+	pr_debug("level: %d, playback: %u, t: %u, dt: %lu\n",
+		 new, mlnxeff->playback_time, t, dt);
+	return new;
+}
+
+static s32 mlnx_calculate_ramp(const struct mlnx_effect *mlnxeff)
+{
+	const struct ff_effect *effect = &mlnxeff->effect;
+	const struct ff_envelope *envelope = mlnx_get_envelope(effect);
+	const unsigned long now = jiffies;
+	const u16 length = effect->replay.length;
+	const s16 mean = (effect->u.ramp.start_level + effect->u.ramp.end_level) / 2;
+	const u16 t = jiffies_to_msecs(now - mlnxeff->begin_at);
+	s32 start = effect->u.ramp.start_level;
+	s32 end = effect->u.ramp.end_level;
+	s32 new;
+
+	if (envelope->attack_length && time_before(now, mlnxeff->attack_stop)) {
+		const s32 clength = jiffies_to_msecs(now - mlnxeff->begin_at);
+		const s32 alength = envelope->attack_length;
+		s32 attack_level;
+		if (end > start)
+			attack_level = mean - envelope->attack_level;
+		else
+			attack_level = mean + envelope->attack_level;
+		start = (start - attack_level) * clength / alength
+		      + attack_level;
+	} else if (envelope->fade_length && time_before_eq(mlnxeff->fade_begin, now)) {
+		const s32 clength = jiffies_to_msecs(now - mlnxeff->fade_begin);
+		const s32 flength = envelope->fade_length;
+		s32 fade_level;
+		if (end > start)
+			fade_level = mean + envelope->fade_level;
+		else
+			fade_level = mean - envelope->fade_level;
+		end = (fade_level - end) * clength / flength + end;
+	}
+
+	new = ((end - start) * t) / length + start;
+	new = clamp(new, -0x7fff, 0x7fff);
+	pr_debug("RAMP level: %d, t: %u\n", new, t);
+	return new;
+}
+
+static void mlnx_destroy(struct ff_device *dev)
+{
+	struct mlnx_device *mlnxdev = dev->private;
+	del_timer_sync(&mlnxdev->timer);
+
+	kfree(mlnxdev->private);
+}
+
+static unsigned long mlnx_get_envelope_update_time(const struct mlnx_effect *mlnxeff,
+						   const unsigned long update_rate_jiffies)
+{
+	const struct ff_effect *effect = &mlnxeff->effect;
+	const struct ff_envelope *envelope = mlnx_get_envelope(effect);
+	const unsigned long now = jiffies;
+	unsigned long fade_next;
+
+	/* Effect has an envelope with nonzero attack time */
+	if (envelope->attack_length && time_before(now, mlnxeff->attack_stop)) {
+		if (time_before(mlnxeff->updated_at + update_rate_jiffies, mlnxeff->attack_stop))
+			return mlnxeff->updated_at + update_rate_jiffies;
+		else
+			return mlnxeff->attack_stop;
+	}
+
+	/* Effect has an envelope with nonzero fade time */
+	if (mlnxeff->effect.replay.length) {
+		if (envelope->fade_length) {
+
+			/* Schedule the next update when the fade begins */
+			if (time_before(mlnxeff->updated_at, mlnxeff->fade_begin))
+				return mlnxeff->fade_begin;
+
+			/* Already fading */
+			else {
+				fade_next = mlnxeff->updated_at
+					  + update_rate_jiffies;
+
+				/* Schedule update when the effect stops */
+				if (time_after(fade_next, mlnxeff->stop_at))
+					return mlnxeff->stop_at;
+				/* Schedule update at the next checkpoint */
+				else
+					return fade_next;
+			}
+		} else
+			return mlnxeff->stop_at;
+	}
+
+	/* There is no envelope */
+
+	/* Prevent the effect from being started twice */
+	if (mlnxeff->begin_at == now && mlnx_is_playing(mlnxeff))
+		return now - 1;
+	else
+		return mlnxeff->begin_at;
+}
+
+static unsigned long mlnx_get_update_time(const struct mlnx_effect *mlnxeff,
+				const unsigned long update_rate_jiffies)
+{
+	const unsigned long now = jiffies;
+	unsigned long time, update_periodic;
+
+	switch (mlnxeff->effect.type) {
+	/* Constant effect does not change with time, but it can have
+	 * an envelope and a duration */
+	case FF_CONSTANT:
+		return mlnx_get_envelope_update_time(mlnxeff,
+						     update_rate_jiffies);
+	/* Periodic and ramp effects have to be periodically updated */
+	case FF_PERIODIC:
+	case FF_RAMP:
+		time = mlnx_get_envelope_update_time(mlnxeff,
+						     update_rate_jiffies);
+
+		if (mlnx_is_square(&mlnxeff->effect)) {
+			const u16 half_T = mlnxeff->effect.u.periodic.period/2;
+			update_periodic = msecs_to_jiffies(half_T)
+					  + mlnxeff->updated_at;
+		} else
+			update_periodic = mlnxeff->updated_at
+					  + update_rate_jiffies;
+
+		/* Periodic effect has to be updated earlier than envelope
+		 * or envelope update time is in the past */
+		if (time_before(update_periodic, time) || time_before(time, now))
+			return update_periodic;
+		else /* Envelope needs to be updated */
+			return time;
+	case FF_DAMPER:
+	case FF_FRICTION:
+	case FF_INERTIA:
+	case FF_SPRING:
+	default:
+		if (time_after_eq(mlnxeff->begin_at, now))
+			return mlnxeff->begin_at;
+		else
+			return mlnxeff->stop_at;
+	}
+}
+
+static void mlnx_schedule_playback(struct mlnx_device *mlnxdev)
+{
+	struct mlnx_effect *mlnxeff;
+	const unsigned long now = jiffies;
+	int events = 0;
+	int i;
+	unsigned long earliest = 0;
+	unsigned long time;
+
+	/* Iterate over all effects and determine the earliest
+	 * time when we have to attend to any */
+	for (i = 0; i < FF_MAX_EFFECTS; i++) {
+		mlnxeff = &mlnxdev->effects[i];
+
+		if (!mlnx_is_started(mlnxeff))
+			continue; /* Effect is not started, skip it */
+
+		if (mlnx_is_playing(mlnxeff))
+			time = mlnx_get_update_time(mlnxeff,
+						mlnxdev->update_rate_jiffies);
+		else
+			time = mlnxeff->begin_at;
+
+		pr_debug("Update time for effect %d: %lu\n", i, time);
+
+		/* Scheduled time is in the future and is either
+		 * before the current earliest time or it is
+		 * the first valid time value in this pass */
+		if (time_before_eq(now, time) &&
+		    (++events == 1 || time_before(time, earliest)))
+			earliest = time;
+	}
+
+	if (events) {
+		pr_debug("Events: %d, earliest: %lu\n", events, earliest);
+		mod_timer(&mlnxdev->timer, earliest);
+	}
+}
+
+static void mlnx_add_force(struct mlnx_effect *mlnxeff, s32 *cfx, s32 *cfy,
+			   const u16 gain)
+{
+	const struct ff_effect *effect = &mlnxeff->effect;
+	u16 direction;
+	s32 level;
+
+	pr_debug("Processing effect type %d, ID %d\n",
+		 mlnxeff->effect.type, mlnxeff->effect.id);
+
+	direction = mlnxeff->effect.direction * 360 / 0xffff;
+	pr_debug("Direction deg: %u\n", direction);
+
+	switch (mlnxeff->effect.type) {
+	case FF_CONSTANT:
+		level = mlnx_apply_envelope(mlnxeff, effect->u.constant.level);
+		break;
+	case FF_PERIODIC:
+		level = mlnx_apply_envelope(mlnxeff,
+					    effect->u.periodic.magnitude);
+		level = mlnx_calculate_periodic(mlnxeff, level);
+		break;
+	case FF_RAMP:
+		level = mlnx_calculate_ramp(mlnxeff);
+		break;
+	default:
+		pr_err("Effect %d not handled by mlnx_add_force!\n",
+		       mlnxeff->effect.type);
+		return;
+	}
+
+	*cfx += mlnx_calculate_x_force(level, direction) * gain / 0xffff;
+	*cfy += mlnx_calculate_y_force(level, direction) * gain / 0xffff;
+}
+
+static void mlnx_play_effects(struct mlnx_device *mlnxdev)
+{
+	const u16 gain = mlnxdev->gain;
+	const unsigned long now = jiffies;
+	int i;
+	int cfx = 0;
+	int cfy = 0;
+
+	for (i = 0; i < FF_MAX_EFFECTS; i++) {
+		struct mlnx_effect *mlnxeff = &mlnxdev->effects[i];
+
+		if (!mlnx_is_started(mlnxeff)) {
+			pr_debug("Effect %hd/%d not started\n",
+				 mlnxeff->effect.id, i);
+			continue;
+		}
+
+		if (time_before(now, mlnxeff->begin_at)) {
+			pr_debug("Effect %hd/%d begins at a later time\n",
+				 mlnxeff->effect.id, i);
+			continue;
+		}
+
+		if (time_before_eq(mlnxeff->stop_at, now) && mlnxeff->effect.replay.length) {
+			pr_debug("Effect %hd/%d has to be stopped\n",
+				 mlnxeff->effect.id, i);
+
+			mlnx_clr_playing(mlnxeff);
+			if (--mlnxeff->repeat > 0)
+				mlnx_restart_effect(mlnxdev, mlnxeff);
+			else {
+				mlnx_clr_started(mlnxeff);
+				mlnx_stop_effect(mlnxdev, mlnxeff);
+			}
+
+			continue;
+		}
+
+		switch (mlnxeff->effect.type) {
+		case FF_CONSTANT:
+		case FF_PERIODIC:
+		case FF_RAMP:
+			if (!mlnx_test_set_playing(mlnxeff)) {
+				mlnxdev->combinable_playing++;
+				pr_debug("Starting combinable effect, total %u\n",
+					 mlnxdev->combinable_playing);
+			}
+			mlnx_add_force(mlnxeff, &cfx, &cfy, gain);
+			break;
+		case FF_DAMPER:
+		case FF_FRICTION:
+		case FF_INERTIA:
+		case FF_SPRING:
+			if (!mlnx_test_set_playing(mlnxeff)) {
+				const struct mlnx_effect_command ecmd = { .cmd = MLNX_START_UNCOMB,
+									  .u.uncomb.id = i,
+									  .u.uncomb.effect = &mlnxeff->effect };
+				mlnxdev->control_effect(mlnxdev->dev,
+						      mlnxdev->private, &ecmd);
+			}
+			break;
+		default:
+			pr_debug("Unhandled type of effect.\n");
+		}
+		mlnxeff->updated_at = now;
+	}
+
+	if (mlnxdev->combinable_playing) {
+		const struct mlnx_effect_command ecmd = { .cmd = MLNX_START_COMBINED,
+							  .u.simple_force = { .x = clamp(cfx, -0x7fff, 0x7fff),
+									      .y = clamp(cfy, -0x7fff, 0x7fff) } };
+		mlnxdev->control_effect(mlnxdev->dev, mlnxdev->private, &ecmd);
+	}
+
+	mlnx_schedule_playback(mlnxdev);
+}
+
+static void mlnx_set_gain(struct input_dev *dev, u16 gain)
+{
+	struct mlnx_device *mlnxdev = dev->ff->private;
+	int i;
+
+	mlnxdev->gain = gain;
+
+	for (i = 0; i < FF_MAX_EFFECTS; i++)
+		mlnx_clr_playing(&mlnxdev->effects[i]);
+
+	mlnx_play_effects(mlnxdev);
+}
+
+static int mlnx_startstop(struct input_dev *dev, int effect_id, int repeat)
+{
+	struct mlnx_device *mlnxdev = dev->ff->private;
+	struct mlnx_effect *mlnxeff = &mlnxdev->effects[effect_id];
+
+	if (repeat > 0) {
+		pr_debug("Starting effect ID %d\n", effect_id);
+		mlnxeff->repeat = repeat;
+		if (!mlnx_is_started(mlnxeff))
+			mlnx_start_effect(mlnxeff);
+	} else {
+		pr_debug("Stopping effect ID %d\n", effect_id);
+		if (mlnx_is_started(mlnxeff)) {
+			if (mlnx_is_playing(mlnxeff)) {
+				mlnx_clr_playing(mlnxeff);
+				mlnx_stop_effect(mlnxdev, mlnxeff);
+			}
+			mlnx_clr_started(mlnxeff);
+		} else {
+			pr_debug("Effect ID %d already stopped.\n", effect_id);
+			return 0;
+		}
+	}
+	mlnx_play_effects(mlnxdev);
+
+	return 0;
+}
+
+static void mlnx_timer_fired(unsigned long data)
+{
+	struct input_dev *dev = (struct input_dev *)data;
+	unsigned long flags;
+
+	spin_lock_irqsave(&dev->event_lock, flags);
+	mlnx_play_effects(dev->ff->private);
+	spin_unlock_irqrestore(&dev->event_lock, flags);
+}
+
+static int mlnx_upload(struct input_dev *dev, struct ff_effect *effect,
+		       struct ff_effect *old)
+{
+	struct mlnx_device *mlnxdev = dev->ff->private;
+	struct mlnx_effect *mlnxeff = &mlnxdev->effects[effect->id];
+	const u16 length = effect->replay.length;
+	const u16 delay = effect->replay.delay;
+	int ret, fade_from;
+
+	/* Effect's timing is below kernel timer resolution */
+	if (length && length < FF_MIN_EFFECT_LENGTH)
+		effect->replay.length = FF_MIN_EFFECT_LENGTH;
+	if (delay && delay < FF_MIN_EFFECT_LENGTH)
+		effect->replay.delay = FF_MIN_EFFECT_LENGTH;
+
+	/* Periodic effects must have a non-zero period */
+	if (effect->type == FF_PERIODIC) {
+		if (!effect->u.periodic.period)
+			return -EINVAL;
+	}
+	/* Ramp effects cannot be infinite */
+	if (effect->type == FF_RAMP && !length)
+		return -EINVAL;
+
+	if (mlnx_is_combinable(effect)) {
+		const struct ff_envelope *envelope = mlnx_get_envelope(effect);
+
+		/* Infinite effects cannot fade */
+		if (!length && envelope->fade_length > 0)
+			return -EINVAL;
+		/* Fade length cannot be greater than effect duration */
+		fade_from = (int)length - (int)envelope->fade_length;
+		if (fade_from < 0)
+			return -EINVAL;
+		/* Envelope cannot start fading before it finishes attacking */
+		if (fade_from < envelope->attack_length && fade_from > 0)
+			return -EINVAL;
+	}
+
+
+	spin_lock_irq(&dev->event_lock);
+	mlnxeff->effect = *effect; /* Keep internal copy of the effect */
+	/* Check if the effect being modified is playing */
+	if (mlnx_is_started(mlnxeff)) {
+		if (mlnx_is_playing(mlnxeff)) {
+			mlnx_clr_playing(mlnxeff);
+			ret = mlnx_restart_effect(mlnxdev, mlnxeff);
+
+			if (ret) {
+				/* Restore the original effect */
+				if (old)
+					mlnxeff->effect = *old;
+				spin_unlock_irq(&dev->event_lock);
+				return ret;
+			}
+		}
+
+		mlnx_schedule_playback(mlnxdev);
+		spin_unlock_irq(&dev->event_lock);
+		return 0;
+	}
+
+	if (mlnx_is_conditional(effect)) {
+		ret = mlnx_upload_conditional(mlnxdev, &mlnxeff->effect);
+		if (ret) {
+			/* Restore the original effect */
+			if (old)
+				mlnxeff->effect = *old;
+			spin_unlock_irq(&dev->event_lock);
+			return ret;
+		}
+	}
+
+	spin_unlock_irq(&dev->event_lock);
+
+	return 0;
+}
+
+int input_ff_create_mlnx(struct input_dev *dev, void *data,
+			 int(*control_effect)(struct input_dev *, void *, const struct mlnx_effect_command *),
+			 const u16 update_rate)
+{
+	struct mlnx_device *mlnxdev;
+	int ret;
+
+	mlnxdev = kzalloc(sizeof(struct mlnx_device), GFP_KERNEL);
+	if (!mlnxdev)
+		return -ENOMEM;
+
+	mlnxdev->dev = dev;
+	mlnxdev->private = data;
+	mlnxdev->control_effect = control_effect;
+	mlnxdev->gain = 0xffff;
+	mlnxdev->update_rate_jiffies = update_rate < FF_MIN_EFFECT_LENGTH ?
+				       FF_MIN_EFFECT_LENGTH : update_rate;
+	setup_timer(&mlnxdev->timer, mlnx_timer_fired, (unsigned long)dev);
+
+	ret = input_ff_create(dev, FF_MAX_EFFECTS);
+	if (ret) {
+		kfree(mlnxdev);
+		return ret;
+	}
+
+	dev->ff->private = mlnxdev;
+	dev->ff->upload = mlnx_upload;
+	dev->ff->set_gain = mlnx_set_gain;
+	dev->ff->destroy = mlnx_destroy;
+	dev->ff->playback = mlnx_startstop;
+
+	pr_debug("MLNX: Device successfully registered.\n");
+	return 0;
+}
+EXPORT_SYMBOL_GPL(input_ff_create_mlnx);
diff --git a/include/linux/input/ff-memless-next.h b/include/linux/input/ff-memless-next.h
new file mode 100644
index 0000000..f2fb080
--- /dev/null
+++ b/include/linux/input/ff-memless-next.h
@@ -0,0 +1,31 @@
+#include <linux/input.h>
+
+enum mlnx_commands {
+	MLNX_START_COMBINED,
+	MLNX_STOP_COMBINED,
+	MLNX_START_UNCOMB,
+	MLNX_STOP_UNCOMB,
+	MLNX_UPLOAD_UNCOMB
+};
+
+struct mlnx_simple_force {
+	const s32 x;
+	const s32 y;
+};
+
+struct mlnx_uncomb_effect {
+	const int id;
+	const struct ff_effect *effect;
+};
+
+struct mlnx_effect_command {
+	const enum mlnx_commands cmd;
+	union {
+		const struct mlnx_simple_force simple_force;
+		const struct mlnx_uncomb_effect uncomb;
+	} u;
+};
+
+int input_ff_create_mlnx(struct input_dev *dev, void *data,
+			 int(*control_effect)(struct input_dev *, void *, const struct mlnx_effect_command *),
+			 const u16 update_rate);
-- 
1.8.5.2