BACKPORT: common: lightbar: Add histeresis to prevent flickering

When ALS is enabled, if light is around one threshold (say 40 lux),
the lightbar will flicker between readings.
Add a histeresis to prevent the flickering.
The current setting is:

setting    ^
(dim)    2 | ------+---->---+
         1 |       +----<---+--->---+
(bright) 0 |                +---<---+---------
           +-------+--------+-------+--------> lux
               20       40      60

BRANCH=smaug, cyan
BUG=chrome-os-partner:44400, b:27849483
TEST=check in a dark room (30~40 lux) there is no flickering.
Add unit test.

Change-Id: I4018e2c2ed764abf9c9ed28e2d50a3e94a7d5f75
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/308205
(cherry picked from commit 81d269dc004b6c7334e4e8eafbb2872e5b6fdcf1)
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/359392

5 files changed, 91 insertions, 20 deletions

diff --git a/common/lightbar.c b/common/lightbar.c
index 3a1e005c9e..94e79fa43d 100644
--- a/common/lightbar.c
+++ b/common/lightbar.c
@@ -195,7 +195,7 @@ static void lightbar_restore_state(void)
 static int last_backlight_level;
 #endif
 #ifdef CONFIG_ALS_LIGHTBAR_DIMMING
-static int last_google_color = -1;
+test_export_static int google_color_id;
 #endif
 
 static int demo_mode = DEMO_MODE_DEFAULT;
@@ -210,18 +210,37 @@ static int quantize_battery_level(int pct)
 }
 
 #ifdef CONFIG_ALS_LIGHTBAR_DIMMING
-static int lux_level_to_google_color(int lux)
+test_export_static int lux_level_to_google_color(const int lux)
 {
 	int i;
 
-	if (!lid_is_open())
+	if (!lid_is_open()) {
 		/* The lid shades the light sensor, use full brightness. */
-		return 0;
+		if (google_color_id != 0) {
+			google_color_id = 0;
+			return 1;
+		} else {
+			return 0;
+		}
+	}
 
-	for (i = 0; i < lb_brightness_levels_count ; i++)
-		if (lux >= lb_brightness_levels[i].lux)
+	/* See if we need to decrease brightness */
+	for (i = google_color_id; i < lb_brightness_levels_count ; i++)
+		if (lux >= lb_brightness_levels[i].lux_down)
+			break;
+	if (i > google_color_id) {
+		google_color_id = i;
+		return 1;
+	}
+	/* See if we need to increase brightness */
+	for (i = google_color_id; i > 0;  i--)
+		if (lux < lb_brightness_levels[i - 1].lux_up)
 			break;
-	return i;
+	if (i < google_color_id) {
+		google_color_id = i;
+		return 1;
+	}
+	return 0;
 }
 #endif
 
@@ -230,9 +249,6 @@ static void get_battery_level(void)
 {
 	int pct = 0;
 	int bl;
-#ifdef CONFIG_ALS_LIGHTBAR_DIMMING
-	int color_id;
-#endif
 
 	if (demo_mode)
 		return;
@@ -282,12 +298,9 @@ static void get_battery_level(void)
 #ifdef CONFIG_ALS_LIGHTBAR_DIMMING
 	/* Read last value (in lux) collected by the motion sensor. */
 	/* Convert lux into brightness percentage */
-	color_id = lux_level_to_google_color(MOTION_SENSE_LUX);
-
-	if (color_id != last_google_color) {
-		last_google_color = pct;
-		memcpy(st.p.color, lb_brightness_levels[color_id].color,
-		       sizeof(lb_brightness_levels[color_id].color));
+	if (lux_level_to_google_color(MOTION_SENSE_LUX)) {
+		memcpy(st.p.color, lb_brightness_levels[google_color_id].color,
+		       sizeof(lb_brightness_levels[google_color_id].color));
 	}
 #endif
 }
diff --git a/include/lightbar.h b/include/lightbar.h
index 8648e3f3bd..61ee5a2a9d 100644
--- a/include/lightbar.h
+++ b/include/lightbar.h
@@ -38,17 +38,19 @@ enum lb_control {
 /*
  * For dimming the lightbar in the dark, we define an array to
  * describe the expected colors:
- * if luminosity is more than 'lux', the color defined will be used.
+ * if luminosity is more than 'lux_up', the color defined will be used.
+ * if luminosity is more than 'lux_down', we will look at the next band.
  * The last entry must have lux == 0.
  * Defining brightness is not enough to prevent washed color in low
  * lux setting.
  */
 struct lb_brightness_def {
-	uint16_t lux;
+	uint16_t lux_up;
+	uint16_t lux_down;
 	struct rgb_s color[4];
 };
 
-extern struct lb_brightness_def lb_brightness_levels[];
+extern const struct lb_brightness_def lb_brightness_levels[];
 extern const unsigned lb_brightness_levels_count;
 #endif
 
diff --git a/include/motion_sense.h b/include/motion_sense.h
index ed24f232fd..aa4170b722 100644
--- a/include/motion_sense.h
+++ b/include/motion_sense.h
@@ -187,6 +187,11 @@ void motion_sense_fifo_add_unit(struct ec_response_motion_sensor_data *data,
 #endif
 
 #ifdef CONFIG_ALS_LIGHTBAR_DIMMING
+#ifdef TEST_BUILD
+#define MOTION_SENSE_LUX 0
+#else
 #define MOTION_SENSE_LUX motion_sensors[CONFIG_ALS_LIGHTBAR_DIMMING].raw_xyz[0]
 #endif
+#endif
+
 #endif /* __CROS_EC_MOTION_SENSE_H */
diff --git a/test/lightbar.c b/test/lightbar.c
index 3aae1e71f3..8a21c1fc62 100644
--- a/test/lightbar.c
+++ b/test/lightbar.c
@@ -11,6 +11,7 @@
 #include "timer.h"
 #include "util.h"
 
+
 static int get_seq(void)
 {
 	int rv;
@@ -272,6 +273,53 @@ static int test_stable_states(void)
 	return EC_SUCCESS;
 }
 
+const struct lb_brightness_def lb_brightness_levels[] = {
+	{
+		/* regular brightness */
+		.lux_up = 60,
+		.lux_down = 40,
+	},
+	{
+		/* 25 - 50% brightness */
+		.lux_up = 40,
+		.lux_down = 20,
+	},
+	{
+		/* 0 .. 25% brightness */
+		.lux_up = 0,
+		.lux_down = 0,
+	},
+};
+const unsigned int lb_brightness_levels_count =
+		ARRAY_SIZE(lb_brightness_levels);
+
+int lux_level_to_google_color(const int lux);
+extern int google_color_id;
+
+int lid_is_open(void)
+{
+	return 1;
+}
+
+static int test_als_lightbar(void)
+{
+	int lux_data[] = { 500, 100, 35, 15, 30, 35, 55, 70, 55, 100 };
+	int exp_gcid[] = {   0,   0,  1,  2,  2,  2,  1,  0,  0,   0 };
+	int exp_chg[]  = {   0,   0,  1,  1,  0,  0,  1,  1,  0,   0 };
+	int i;
+
+	BUILD_ASSERT(ARRAY_SIZE(lux_data) == ARRAY_SIZE(exp_gcid));
+	BUILD_ASSERT(ARRAY_SIZE(lux_data) == ARRAY_SIZE(exp_chg));
+
+	google_color_id = 0;
+	for (i = 0; i < ARRAY_SIZE(lux_data); i++) {
+		TEST_ASSERT(exp_chg[i] ==
+			    lux_level_to_google_color(lux_data[i]));
+		TEST_ASSERT(exp_gcid[i] == google_color_id);
+	}
+	return EC_SUCCESS;
+}
+
 void run_test(void)
 {
 	RUN_TEST(test_stable_states);
@@ -280,5 +328,6 @@ void run_test(void)
 	RUN_TEST(test_stop_timeout);
 	RUN_TEST(test_oneshots_norm_msg);
 	RUN_TEST(test_double_oneshots);
+	RUN_TEST(test_als_lightbar);
 	test_print_result();
 }
diff --git a/test/test_config.h b/test/test_config.h
index 8cdb12d1d8..0b1608001d 100644
--- a/test/test_config.h
+++ b/test/test_config.h
@@ -103,7 +103,9 @@ int bd99992gw_get_temp(uint16_t adc);
 #endif
 
 #ifdef TEST_LIGHTBAR
-#define I2C_PORT_LIGHTBAR 1
+#define CONFIG_I2C
+#define I2C_PORT_LIGHTBAR 0
+#define CONFIG_ALS_LIGHTBAR_DIMMING 0
 #endif
 
 #ifdef TEST_USB_PD