Fix: auto brightness decrease curve not smooth enough while moving to a dark environment

We reduced the period to read ALS value, also modified the granularity
to match the MS requriement.

Signed-off-by: Josh Tsai <josh_tsai@compal.corp-partner.google.com>

Author: Josh Tsai

board/hx30/board.h

@@ -160,6 +160,7 @@
 /* Optional features */
 #define CONFIG_ALS
 #define CONFIG_CMD_ALS
+#define ALS_POLL_PERIOD (50 * MSEC)
 
 #define CONFIG_BATTERY_CUT_OFF
 #define CONFIG_BATTERY_SMART

board/hx30/i2c_hid_mediakeys.c

@@ -355,6 +355,7 @@ static int als_polling_mode_count;
 void report_illuminance_value(void)
 {
 	uint16_t newIlluminaceValue = *(uint16_t *)host_get_memmap(EC_MEMMAP_ALS);
+	static int granularity;
 
 	/* We need to polling the ALS value at least 6 seconds */
 	if (als_polling_mode_count <= 60) {
@@ -365,7 +366,7 @@ void report_illuminance_value(void)
 		task_set_event(TASK_ID_HID, ((1 << HID_ALS_REPORT_LUX) |
 			EVENT_REPORT_ILLUMINANCE_VALUE), 0);
 	} else {
-		if (ABS(als_sensor.illuminanceValue - newIlluminaceValue) > 5) {
+		if (ABS(als_sensor.illuminanceValue - newIlluminaceValue) > granularity) {
 			als_sensor.illuminanceValue = newIlluminaceValue;
 			task_set_event(TASK_ID_HID, ((1 << HID_ALS_REPORT_LUX) |
 				EVENT_REPORT_ILLUMINANCE_VALUE), 0);
@@ -374,6 +375,18 @@ void report_illuminance_value(void)
 		}
 	}
 
+	/**
+	 * To ensure the best experience the ALS should have a granularity of
+	 * at most 1 lux when the ambient light is below 25 lux and a granularity
+	 * of at most 4% of the ambient light when it is above 25 lux.
+	 * This enable the adaptive brightness algorithm to perform smooth screen
+	 * brightness transitions.
+	 */
+	if (newIlluminaceValue < 25)
+		granularity = 1;
+	else
+		granularity = newIlluminaceValue*4/100;
+
 }
 DECLARE_DEFERRED(report_illuminance_value);
 

common/als.c

@@ -22,8 +22,9 @@
 #define CPRINTS(format, args...) cprints(CC_ALS, format, ## args)
 #define CPRINTF(format, args...) cprintf(CC_ALS, format, ## args)
 
-
+#ifndef ALS_POLL_PERIOD
 #define ALS_POLL_PERIOD SECOND
+#endif
 
 static int task_timeout = -1;