mkbp: Separate FIFO from the keyboard driver

Move protocol-related functionality out from the keyboard driver. This
change is required to allow passing button events via MKBP on devices with
non-MKBP keyboards. It reorganizes the code without changing the logic.

BUG=b:170966461
BRANCH=main,firmware-dedede-13606.B,firmware-volteer-13672.B-main
TEST=None

Signed-off-by: Boris Mittelberg <bmbm@google.com>
Change-Id: Ifb5b9d8e605f491313ee1dfe2c9950eb52152aa8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2669355

10 files changed, 319 insertions, 244 deletions

diff --git a/common/build.mk b/common/build.mk
index 3ca7a0fa56..aea81a9a29 100644
--- a/common/build.mk
+++ b/common/build.mk
@@ -95,7 +95,7 @@ common-$(CONFIG_I2C_VIRTUAL_BATTERY)+=virtual_battery.o
 common-$(CONFIG_INDUCTIVE_CHARGING)+=inductive_charging.o
 common-$(CONFIG_KEYBOARD_PROTOCOL_8042)+=keyboard_8042.o \
 	keyboard_8042_sharedlib.o
-common-$(CONFIG_KEYBOARD_PROTOCOL_MKBP)+=keyboard_mkbp.o
+common-$(CONFIG_KEYBOARD_PROTOCOL_MKBP)+=keyboard_mkbp.o mkbp_fifo.o
 common-$(CONFIG_KEYBOARD_TEST)+=keyboard_test.o
 common-$(CONFIG_KEYBOARD_VIVALDI)+=keyboard_vivaldi.o
 common-$(CONFIG_LED_COMMON)+=led_common.o
diff --git a/common/keyboard_mkbp.c b/common/keyboard_mkbp.c
index 4cd92f7041..58a55477f0 100644
--- a/common/keyboard_mkbp.c
+++ b/common/keyboard_mkbp.c
@@ -23,6 +23,7 @@
 #include "keyboard_test.h"
 #include "lid_switch.h"
 #include "mkbp_event.h"
+#include "mkbp_fifo.h"
 #include "power_button.h"
 #include "system.h"
 #include "tablet_mode.h"
@@ -34,17 +35,6 @@
 #define CPUTS(outstr) cputs(CC_KEYBOARD, outstr)
 #define CPRINTS(format, args...) cprints(CC_KEYBOARD, format, ## args)
 
-/*
- * Common FIFO depth.  This needs to be big enough not to overflow if a
- * series of keys is pressed in rapid succession and the kernel is too busy
- * to read them out right away.
- *
- * RAM usage is (depth * #cols); A 16-entry FIFO will consume 16x13=208 bytes,
- * which is non-trivial but not horrible.
- */
-
-#define FIFO_DEPTH 16
-
 /* Changes to col,row here need to also be reflected in kernel.
  * drivers/input/mkbp.c ... see KEY_BATTERY.
  */
@@ -52,21 +42,6 @@
 #define BATTERY_KEY_ROW 7
 #define BATTERY_KEY_ROW_MASK BIT(BATTERY_KEY_ROW)
 
-static uint32_t fifo_start;	/* first entry */
-static uint32_t fifo_end;	/* last entry */
-static uint32_t fifo_entries;	/* number of existing entries */
-static struct ec_response_get_next_event fifo[FIFO_DEPTH];
-/*
- * Mutex for critical sections of mkbp_fifo_add(), which is called
- * from various tasks.
- */
-K_MUTEX_DEFINE(fifo_add_mutex);
-/*
- * Mutex for critical sections of fifo_remove(), which is called from the
- * hostcmd task and from keyboard_clear_buffer().
- */
-K_MUTEX_DEFINE(fifo_remove_mutex);
-
 /* Button and switch state. */
 static uint32_t mkbp_button_state;
 static uint32_t mkbp_switch_state;
@@ -97,172 +72,24 @@ static struct ec_mkbp_protocol_config config = {
 	.fifo_max_depth = FIFO_DEPTH,
 };
 
-static int get_data_size(enum ec_mkbp_event e)
-{
-	switch (e) {
-	case EC_MKBP_EVENT_KEY_MATRIX:
-		return keyboard_cols;
-
-#ifdef CONFIG_HOST_EVENT64
-	case EC_MKBP_EVENT_HOST_EVENT64:
-		return sizeof(uint64_t);
-#endif
-
-	case EC_MKBP_EVENT_HOST_EVENT:
-	case EC_MKBP_EVENT_BUTTON:
-	case EC_MKBP_EVENT_SWITCH:
-	case EC_MKBP_EVENT_SYSRQ:
-		return sizeof(uint32_t);
-	default:
-		/* For unknown types, say it's 0. */
-		return 0;
-	}
-}
-
-/**
- * Pop MKBP event data from FIFO
- *
- * @return EC_SUCCESS if entry popped, EC_ERROR_UNKNOWN if FIFO is empty
- */
-static int fifo_remove(uint8_t *buffp)
-{
-	int size;
-
-	mutex_lock(&fifo_remove_mutex);
-	if (!fifo_entries) {
-		/* no entry remaining in FIFO : return last known state */
-		int last = (fifo_start + FIFO_DEPTH - 1) % FIFO_DEPTH;
-
-		size = get_data_size(fifo[last].event_type);
-
-		memcpy(buffp, &fifo[last].data, size);
-		mutex_unlock(&fifo_remove_mutex);
-
-		/*
-		 * Bail out without changing any FIFO indices and let the
-		 * caller know something strange happened. The buffer will
-		 * will contain the last known state of the keyboard.
-		 */
-		return EC_ERROR_UNKNOWN;
-	}
-
-	/* Return just the event data. */
-	if (buffp) {
-		size = get_data_size(fifo[fifo_start].event_type);
-		/* skip over event_type. */
-		memcpy(buffp, &fifo[fifo_start].data, size);
-	}
-
-	fifo_start = (fifo_start + 1) % FIFO_DEPTH;
-	atomic_sub(&fifo_entries, 1);
-	mutex_unlock(&fifo_remove_mutex);
-
-	return EC_SUCCESS;
-}
-
 /*****************************************************************************/
 /* Interface */
 
 void keyboard_clear_buffer(void)
 {
-	int i, new_fifo_entries = 0;
-
-	CPRINTS("clear keyboard MKBP fifo");
-
-	/*
-	 * Order of these locks is important to prevent deadlock since
-	 * mkbp_fifo_add() may call fifo_remove().
-	 */
-	mutex_lock(&fifo_add_mutex);
-	mutex_lock(&fifo_remove_mutex);
-
-	/* Reset the end position */
-	fifo_end = fifo_start;
-
-	for (i = 0; i < fifo_entries; i++) {
-		int cur = (fifo_start + i) % FIFO_DEPTH;
-
-		/* Drop keyboard events */
-		if (fifo[cur].event_type == EC_MKBP_EVENT_KEY_MATRIX)
-			continue;
-
-		/* And move other events to the front */
-		memmove(&fifo[fifo_end], &fifo[cur], sizeof(fifo[cur]));
-		fifo_end = (fifo_end + 1) % FIFO_DEPTH;
-		++new_fifo_entries;
-	}
-	fifo_entries = new_fifo_entries;
-
-	mutex_unlock(&fifo_remove_mutex);
-	mutex_unlock(&fifo_add_mutex);
-}
-
-void mkbp_clear_fifo(void)
-{
-	int i;
-
-	CPRINTS("clear MKBP fifo");
-
-	/*
-	 * Order of these locks is important to prevent deadlock since
-	 * mkbp_fifo_add() may call fifo_remove().
-	 */
-	mutex_lock(&fifo_add_mutex);
-	mutex_lock(&fifo_remove_mutex);
-
-	fifo_start = 0;
-	fifo_end = 0;
-	/* This assignment is safe since both mutexes are held. */
-	fifo_entries = 0;
-	for (i = 0; i < FIFO_DEPTH; i++)
-		memset(&fifo[i], 0, sizeof(struct ec_response_get_next_event));
-
-	mutex_unlock(&fifo_remove_mutex);
-	mutex_unlock(&fifo_add_mutex);
-}
-
-test_mockable int keyboard_fifo_add(const uint8_t *buffp)
-{
-	return mkbp_fifo_add((uint8_t)EC_MKBP_EVENT_KEY_MATRIX, buffp);
+	mkbp_fifo_clear_keyboard();
 }
 
-test_mockable int mkbp_fifo_add(uint8_t event_type, const uint8_t *buffp)
+test_mockable int mkbp_keyboard_add(const uint8_t *buffp)
 {
-	uint8_t size;
-
 	/*
-	 * If the data is a keyboard matrix and the keyboard protocol is not
-	 * enabled, don't save the state to the FIFO or trigger an interrupt.
+	 * If the keyboard protocol is not enabled, don't save the state to
+	 * the FIFO or trigger an interrupt.
 	 */
-	if (!(config.flags & EC_MKBP_FLAGS_ENABLE) &&
-	    (event_type == EC_MKBP_EVENT_KEY_MATRIX))
+	if (!(config.flags & EC_MKBP_FLAGS_ENABLE))
 		return EC_SUCCESS;
 
-	mutex_lock(&fifo_add_mutex);
-	if (fifo_entries >= config.fifo_max_depth) {
-		mutex_unlock(&fifo_add_mutex);
-		CPRINTS("MKBP common FIFO depth %d reached",
-			config.fifo_max_depth);
-
-		return EC_ERROR_OVERFLOW;
-	}
-
-	size = get_data_size(event_type);
-	fifo[fifo_end].event_type = event_type;
-	memcpy(&fifo[fifo_end].data, buffp, size);
-	fifo_end = (fifo_end + 1) % FIFO_DEPTH;
-	atomic_add(&fifo_entries, 1);
-
-	/*
-	 * If our event didn't generate an interrupt then the host is still
-	 * asleep. In this case, we don't want to queue our event, except if
-	 * another event just woke the host (and wake is already in progress).
-	 */
-	if (!mkbp_send_event(event_type) && fifo_entries == 1)
-		fifo_remove(NULL);
-
-	mutex_unlock(&fifo_add_mutex);
-	return EC_SUCCESS;
+	return mkbp_fifo_add((uint8_t)EC_MKBP_EVENT_KEY_MATRIX, buffp);
 }
 
 void mkbp_update_switches(uint32_t sw, int state)
@@ -378,64 +205,28 @@ DECLARE_HOOK(HOOK_POWER_BUTTON_CHANGE, keyboard_power_button,
 	     HOOK_PRIO_DEFAULT);
 #endif /* defined(CONFIG_POWER_BUTTON) */
 
-static int get_next_event(uint8_t *out, enum ec_mkbp_event evt)
-{
-	uint8_t t = fifo[fifo_start].event_type;
-	uint8_t size;
-
-	if (!fifo_entries)
-		return -1;
-
-	/*
-	 * We need to peek at the next event to check that we were called with
-	 * the correct event.
-	 */
-	if (t != (uint8_t)evt) {
-		/*
-		 * We were called with the wrong event.  The next element in the
-		 * FIFO's event type doesn't match with what we were called
-		 * with.  Return an error that we're busy.  The caller will need
-		 * to call us with the correct event first.
-		 */
-		return -EC_ERROR_BUSY;
-	}
-
-	fifo_remove(out);
-
-	/* Keep sending events if FIFO is not empty */
-	if (fifo_entries)
-		mkbp_send_event(fifo[fifo_start].event_type);
-
-	/* Return the correct size of the data. */
-	size = get_data_size(t);
-	if (size)
-		return size;
-	else
-		return -EC_ERROR_UNKNOWN;
-}
-
 static int keyboard_get_next_event(uint8_t *out)
 {
-	return get_next_event(out, EC_MKBP_EVENT_KEY_MATRIX);
+	return mkbp_fifo_get_next_event(out, EC_MKBP_EVENT_KEY_MATRIX);
 }
 DECLARE_EVENT_SOURCE(EC_MKBP_EVENT_KEY_MATRIX, keyboard_get_next_event);
 
 static int button_get_next_event(uint8_t *out)
 {
-	return get_next_event(out, EC_MKBP_EVENT_BUTTON);
+	return mkbp_fifo_get_next_event(out, EC_MKBP_EVENT_BUTTON);
 }
 DECLARE_EVENT_SOURCE(EC_MKBP_EVENT_BUTTON, button_get_next_event);
 
 static int switch_get_next_event(uint8_t *out)
 {
-	return get_next_event(out, EC_MKBP_EVENT_SWITCH);
+	return mkbp_fifo_get_next_event(out, EC_MKBP_EVENT_SWITCH);
 }
 DECLARE_EVENT_SOURCE(EC_MKBP_EVENT_SWITCH, switch_get_next_event);
 
 #ifdef CONFIG_EMULATED_SYSRQ
 static int sysrq_get_next_event(uint8_t *out)
 {
-	return get_next_event(out, EC_MKBP_EVENT_SYSRQ);
+	return mkbp_fifo_get_next_event(out, EC_MKBP_EVENT_SYSRQ);
 }
 DECLARE_EVENT_SOURCE(EC_MKBP_EVENT_SYSRQ, sysrq_get_next_event);
 #endif
@@ -450,7 +241,7 @@ void keyboard_send_battery_key(void)
 
 	/* Add to FIFO only if AP is on or else it will wake from suspend */
 	if (chipset_in_state(CHIPSET_STATE_ON))
-		keyboard_fifo_add(state);
+		mkbp_keyboard_add(state);
 }
 
 void clear_typematic_key(void)
@@ -591,7 +382,7 @@ static void simulate_key(int row, int col, int pressed)
 	if (pressed)
 		simulated_key[col] |= BIT(row);
 
-	keyboard_fifo_add(simulated_key);
+	mkbp_keyboard_add(simulated_key);
 }
 
 static int command_mkbp_keyboard_press(int argc, char **argv)
@@ -736,6 +527,8 @@ host_command_mkbp_set_config(struct host_cmd_handler_args *args)
 			    config.valid_mask & req->config.valid_mask,
 			    config.valid_flags & req->config.valid_flags);
 
+	mkbp_fifo_depth_update(config.fifo_max_depth);
+
 	return EC_RES_SUCCESS;
 }
 DECLARE_HOST_COMMAND(EC_CMD_MKBP_SET_CONFIG,
diff --git a/common/keyboard_scan.c b/common/keyboard_scan.c
index e5de132197..bb3ee2a8df 100644
--- a/common/keyboard_scan.c
+++ b/common/keyboard_scan.c
@@ -600,7 +600,7 @@ static int check_keys_changed(uint8_t *state)
 #endif
 
 #ifdef CONFIG_KEYBOARD_PROTOCOL_MKBP
-		keyboard_fifo_add(state);
+		mkbp_keyboard_add(state);
 #endif
 	}
 
diff --git a/common/mkbp_event.c b/common/mkbp_event.c
index ac922613d8..d67951c3b3 100644
--- a/common/mkbp_event.c
+++ b/common/mkbp_event.c
@@ -197,7 +197,7 @@ static inline int host_is_sleeping(void)
 /*
  * This is the deferred function that ensures that we attempt to set the MKBP
  * interrupt again if there was a failure in the system (EC or AP) and the AP
- * never called get_next_event.
+ * never called mkbp_fifo_get_next_event.
  */
 static void force_mkbp_if_events(void);
 DECLARE_DEFERRED(force_mkbp_if_events);
@@ -272,7 +272,7 @@ static void activate_mkbp_with_events(uint32_t events_to_add)
 /*
  * This is the deferred function that ensures that we attempt to set the MKBP
  * interrupt again if there was a failure in the system (EC or AP) and the AP
- * never called get_next_event.
+ * never called mkbp_fifo_get_next_event.
  */
 static void force_mkbp_if_events(void)
 {
diff --git a/common/mkbp_fifo.c b/common/mkbp_fifo.c
new file mode 100644
index 0000000000..428d6412fc
--- /dev/null
+++ b/common/mkbp_fifo.c
@@ -0,0 +1,241 @@
+/* Copyright 2021 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Matrix KeyBoard Protocol FIFO buffer implementation
+ */
+
+#include "atomic.h"
+#include "common.h"
+#include "keyboard_config.h"
+#include "mkbp_event.h"
+#include "mkbp_fifo.h"
+#include "system.h"
+#include "task.h"
+#include "util.h"
+
+/* Console output macros */
+#define CPRINTS(format, args...) cprints(CC_KEYBOARD, format, ## args)
+
+/*
+ * Common FIFO depth.  This needs to be big enough not to overflow if a
+ * series of keys is pressed in rapid succession and the kernel is too busy
+ * to read them out right away.
+ *
+ * RAM usage is (depth * #cols); A 16-entry FIFO will consume 16x13=208 bytes,
+ * which is non-trivial but not horrible.
+ */
+
+static uint32_t fifo_start;	/* first entry */
+static uint32_t fifo_end;	/* last entry */
+static uint32_t fifo_entries;	/* number of existing entries */
+static uint8_t fifo_max_depth = FIFO_DEPTH;
+static struct ec_response_get_next_event fifo[FIFO_DEPTH];
+
+/*
+ * Mutex for critical sections of mkbp_fifo_add(), which is called
+ * from various tasks.
+ */
+K_MUTEX_DEFINE(fifo_add_mutex);
+/*
+ * Mutex for critical sections of fifo_remove(), which is called from the
+ * hostcmd task and from keyboard_clear_buffer().
+ */
+K_MUTEX_DEFINE(fifo_remove_mutex);
+
+static int get_data_size(enum ec_mkbp_event e)
+{
+	switch (e) {
+	case EC_MKBP_EVENT_KEY_MATRIX:
+		return KEYBOARD_COLS_MAX;
+
+#ifdef CONFIG_HOST_EVENT64
+	case EC_MKBP_EVENT_HOST_EVENT64:
+		return sizeof(uint64_t);
+#endif
+
+	case EC_MKBP_EVENT_HOST_EVENT:
+	case EC_MKBP_EVENT_BUTTON:
+	case EC_MKBP_EVENT_SWITCH:
+	case EC_MKBP_EVENT_SYSRQ:
+		return sizeof(uint32_t);
+	default:
+		/* For unknown types, say it's 0. */
+		return 0;
+	}
+}
+
+/**
+ * Pop MKBP event data from FIFO
+ *
+ * @return EC_SUCCESS if entry popped, EC_ERROR_UNKNOWN if FIFO is empty
+ */
+static int fifo_remove(uint8_t *buffp)
+{
+	int size;
+
+	mutex_lock(&fifo_remove_mutex);
+	if (!fifo_entries) {
+		/* no entry remaining in FIFO : return last known state */
+		int last = (fifo_start + FIFO_DEPTH - 1) % FIFO_DEPTH;
+
+		size = get_data_size(fifo[last].event_type);
+
+		memcpy(buffp, &fifo[last].data, size);
+		mutex_unlock(&fifo_remove_mutex);
+
+		/*
+		 * Bail out without changing any FIFO indices and let the
+		 * caller know something strange happened. The buffer will
+		 * will contain the last known state of the keyboard.
+		 */
+		return EC_ERROR_UNKNOWN;
+	}
+
+	/* Return just the event data. */
+	if (buffp) {
+		size = get_data_size(fifo[fifo_start].event_type);
+		/* skip over event_type. */
+		memcpy(buffp, &fifo[fifo_start].data, size);
+	}
+
+	fifo_start = (fifo_start + 1) % FIFO_DEPTH;
+	atomic_sub(&fifo_entries, 1);
+	mutex_unlock(&fifo_remove_mutex);
+
+	return EC_SUCCESS;
+}
+
+/*****************************************************************************/
+/* Interface */
+
+void mkbp_fifo_depth_update(uint8_t new_max_depth)
+{
+	fifo_max_depth = new_max_depth;
+}
+
+
+void mkbp_fifo_clear_keyboard(void)
+{
+	int i, new_fifo_entries = 0;
+
+	CPRINTS("clear keyboard MKBP fifo");
+
+	/*
+	 * Order of these locks is important to prevent deadlock since
+	 * mkbp_fifo_add() may call fifo_remove().
+	 */
+	mutex_lock(&fifo_add_mutex);
+	mutex_lock(&fifo_remove_mutex);
+
+	/* Reset the end position */
+	fifo_end = fifo_start;
+
+	for (i = 0; i < fifo_entries; i++) {
+		int cur = (fifo_start + i) % FIFO_DEPTH;
+
+		/* Drop keyboard events */
+		if (fifo[cur].event_type == EC_MKBP_EVENT_KEY_MATRIX)
+			continue;
+
+		/* And move other events to the front */
+		memmove(&fifo[fifo_end], &fifo[cur], sizeof(fifo[cur]));
+		fifo_end = (fifo_end + 1) % FIFO_DEPTH;
+		++new_fifo_entries;
+	}
+	fifo_entries = new_fifo_entries;
+
+	mutex_unlock(&fifo_remove_mutex);
+	mutex_unlock(&fifo_add_mutex);
+}
+
+void mkbp_clear_fifo(void)
+{
+	int i;
+
+	CPRINTS("clear MKBP fifo");
+
+	/*
+	 * Order of these locks is important to prevent deadlock since
+	 * mkbp_fifo_add() may call fifo_remove().
+	 */
+	mutex_lock(&fifo_add_mutex);
+	mutex_lock(&fifo_remove_mutex);
+
+	fifo_start = 0;
+	fifo_end = 0;
+	/* This assignment is safe since both mutexes are held. */
+	fifo_entries = 0;
+	for (i = 0; i < FIFO_DEPTH; i++)
+		memset(&fifo[i], 0, sizeof(struct ec_response_get_next_event));
+
+	mutex_unlock(&fifo_remove_mutex);
+	mutex_unlock(&fifo_add_mutex);
+}
+
+test_mockable int mkbp_fifo_add(uint8_t event_type, const uint8_t *buffp)
+{
+	uint8_t size;
+
+	mutex_lock(&fifo_add_mutex);
+	if (fifo_entries >= fifo_max_depth) {
+		mutex_unlock(&fifo_add_mutex);
+		CPRINTS("MKBP common FIFO depth %d reached",
+			fifo_max_depth);
+
+		return EC_ERROR_OVERFLOW;
+	}
+
+	size = get_data_size(event_type);
+	fifo[fifo_end].event_type = event_type;
+	memcpy(&fifo[fifo_end].data, buffp, size);
+	fifo_end = (fifo_end + 1) % FIFO_DEPTH;
+	atomic_add(&fifo_entries, 1);
+
+	/*
+	 * If our event didn't generate an interrupt then the host is still
+	 * asleep. In this case, we don't want to queue our event, except if
+	 * another event just woke the host (and wake is already in progress).
+	 */
+	if (!mkbp_send_event(event_type) && fifo_entries == 1)
+		fifo_remove(NULL);
+
+	mutex_unlock(&fifo_add_mutex);
+	return EC_SUCCESS;
+}
+
+int mkbp_fifo_get_next_event(uint8_t *out, enum ec_mkbp_event evt)
+{
+	uint8_t t = fifo[fifo_start].event_type;
+	uint8_t size;
+
+	if (!fifo_entries)
+		return -1;
+
+	/*
+	 * We need to peek at the next event to check that we were called with
+	 * the correct event.
+	 */
+	if (t != (uint8_t)evt) {
+		/*
+		 * We were called with the wrong event.  The next element in the
+		 * FIFO's event type doesn't match with what we were called
+		 * with.  Return an error that we're busy.  The caller will need
+		 * to call us with the correct event first.
+		 */
+		return -EC_ERROR_BUSY;
+	}
+
+	fifo_remove(out);
+
+	/* Keep sending events if FIFO is not empty */
+	if (fifo_entries)
+		mkbp_send_event(fifo[fifo_start].event_type);
+
+	/* Return the correct size of the data. */
+	size = get_data_size(t);
+	if (size)
+		return size;
+	else
+		return -EC_ERROR_UNKNOWN;
+}
diff --git a/include/keyboard_mkbp.h b/include/keyboard_mkbp.h
index cc1dec04b2..c0fe0a842d 100644
--- a/include/keyboard_mkbp.h
+++ b/include/keyboard_mkbp.h
@@ -16,21 +16,7 @@
  *
  * @return EC_SUCCESS if entry added, EC_ERROR_OVERFLOW if FIFO is full
  */
-int keyboard_fifo_add(const uint8_t *buffp);
-
-/**
- * Add an element to the common MKBP FIFO.
- *
- * @param event_type	The MKBP event type.
- * @param buffp		Pointer to the event data to enqueue.
- * @return EC_SUCCESS if entry added, EC_ERROR_OVERFLOW if FIFO is full.
- */
-int mkbp_fifo_add(uint8_t event_type, const uint8_t *buffp);
-
-/**
- * Clear the MKBP common FIFO.
- */
-void mkbp_clear_fifo(void);
+int mkbp_keyboard_add(const uint8_t *buffp);
 
 /**
  * Send KEY_BATTERY keystroke.
diff --git a/include/mkbp_fifo.h b/include/mkbp_fifo.h
new file mode 100644
index 0000000000..347f94e2a7
--- /dev/null
+++ b/include/mkbp_fifo.h
@@ -0,0 +1,54 @@
+/* Copyright 2021 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* FIFO buffer of MKBP events for Chrome EC */
+
+#ifndef __CROS_EC_MKBP_FIFO_H
+#define __CROS_EC_MKBP_FIFO_H
+
+#include "common.h"
+#include "ec_commands.h"
+
+
+#define FIFO_DEPTH 16
+
+
+/**
+ * Update the "soft" FIFO depth (size). The new depth should be less or
+ * equal FIFO_DEPTH
+ *
+ * @param new_max_depth		New FIFO depth.
+ */
+void mkbp_fifo_depth_update(uint8_t new_max_depth);
+
+/**
+ * Clear all keyboard events from the MKBP common FIFO
+ */
+void mkbp_fifo_clear_keyboard(void);
+
+/**
+ * Clear the entire MKBP common FIFO.
+ */
+void mkbp_clear_fifo(void);
+
+/**
+ * Add an element to the common MKBP FIFO.
+ *
+ * @param event_type	The MKBP event type.
+ * @param buffp		Pointer to the event data to enqueue.
+ * @return EC_SUCCESS if entry added, EC_ERROR_OVERFLOW if FIFO is full.
+ */
+test_mockable int mkbp_fifo_add(uint8_t event_type, const uint8_t *buffp);
+
+/**
+ * Remove an element from the common MKBP FIFO.
+ *
+ * @param out		Pointer to the event data to dequeue.
+ * @param event_type	The MKBP event type.
+ * @return size of the returned event, EC_ERROR_BUSY if type mismatch.
+ */
+int mkbp_fifo_get_next_event(uint8_t *out, enum ec_mkbp_event evt);
+
+#endif /* __CROS_EC_MKBP_FIFO_H */
diff --git a/test/kb_mkbp.c b/test/kb_mkbp.c
index 6ab010807d..3b191a47ac 100644
--- a/test/kb_mkbp.c
+++ b/test/kb_mkbp.c
@@ -65,7 +65,7 @@ int press_key(int c, int r, int pressed)
 {
 	ccprintf("Input %s (%d, %d)\n", action[pressed], c, r);
 	set_state(c, r, pressed);
-	return keyboard_fifo_add(state);
+	return mkbp_keyboard_add(state);
 }
 
 int verify_key(int c, int r, int pressed)
diff --git a/test/kb_scan.c b/test/kb_scan.c
index e0ba11137d..a4fb6f9841 100644
--- a/test/kb_scan.c
+++ b/test/kb_scan.c
@@ -77,7 +77,7 @@ int keyboard_raw_read_rows(void)
 	}
 }
 
-int keyboard_fifo_add(const uint8_t *buffp)
+int mkbp_keyboard_add(const uint8_t *buffp)
 {
 	fifo_add_count++;
 	return EC_SUCCESS;
diff --git a/zephyr/CMakeLists.txt b/zephyr/CMakeLists.txt
index badd503e2f..2b3e0d7233 100644
--- a/zephyr/CMakeLists.txt
+++ b/zephyr/CMakeLists.txt
@@ -288,7 +288,8 @@ zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_KEYBOARD_PROTOCOL_8042
                                                 "${PLATFORM_EC}/common/keyboard_8042.c"
                                                 "${PLATFORM_EC}/common/keyboard_8042_sharedlib.c")
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_KEYBOARD_PROTOCOL_MKBP
-                                                "${PLATFORM_EC}/common/keyboard_mkbp.c")
+                                                "${PLATFORM_EC}/common/keyboard_mkbp.c"
+                                                "${PLATFORM_EC}/common/mkbp_fifo.c")
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_KEYBOARD_VIVALDI
                                                 "${PLATFORM_EC}/common/keyboard_vivaldi.c")
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_PWM_KBLIGHT