charge_state_v2: Simplify low-battery base power logic

When the base battery is low, we need to provide it with some power,
to make sure the battery does not fully deplete.

Instead of relying on a separate configuration value, we simply
reuse min_base_system_power. Also, we fix a bug that incorrectly
used a power value as current.

BRANCH=none
BUG=b:71881017
BUG=b:74414928
TEST=With a critically low wand (3%), lux is able to provide
     enough power to charge wand battery a little (44mA), even
     when backlight is fully on, and touchpad is in use.

Change-Id: I3174ac273712eeb83ce1283dda3d786ad503e6f3
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/956661
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

1 files changed, 13 insertions, 8 deletions

diff --git a/common/charge_state_v2.c b/common/charge_state_v2.c
index f375404aee..9e1db52790 100644
--- a/common/charge_state_v2.c
+++ b/common/charge_state_v2.c
@@ -150,8 +150,6 @@ struct dual_battery_policy {
 	uint16_t otg_voltage;
 	/* Maximum current to apply from base to lid (mA) */
 	uint16_t max_base_to_lid_current;
-	/* When base battery is low, current to provide from lid to base (mA) */
-	uint16_t lid_to_base_current_charge_base_low;
 	/*
 	 * Margin to apply between provided OTG output current and input current
 	 * limit, to make sure that input charger does not overcurrent output
@@ -170,7 +168,9 @@ struct dual_battery_policy {
 	uint8_t max_charge_lid_batt_to_batt;
 
 	/*** Policies when AC is connected. ***/
-	/* Minimum power to allocate to base (mW) */
+	/* Minimum power to allocate to base (mW), includes some margin to allow
+	 * base to charge when critically low.
+	 */
 	uint16_t min_base_system_power;
 
 	/* Smoothing factor for lid power (/128) */
@@ -197,12 +197,11 @@ struct dual_battery_policy {
 static const struct dual_battery_policy db_policy = {
 	.otg_voltage = 12000, /* mV */
 	.max_base_to_lid_current = 1800, /* mA, about 2000mA with margin. */
-	.lid_to_base_current_charge_base_low = 200, /* mA, so about 3W. */
 	.margin_otg_current = 13, /* /128 = 10.1% */
 	.min_charge_base_otg = 5, /* % */
 	.max_charge_base_batt_to_batt = 4, /* % */
 	.max_charge_lid_batt_to_batt = 10, /* % */
-	.min_base_system_power = 1100, /* mW */
+	.min_base_system_power = 1300, /* mW */
 	.lid_system_power_smooth = 32, /* 32/128 = 0.25 */
 	.battery_power_smooth = 1, /* 1/128 = 0.008 */
 	.margin_base_battery_power = 32, /* 32/128 = 0.25 */
@@ -484,14 +483,20 @@ static void charge_allocate_input_current_limit(void)
 		} else {
 			/*
 			 * Base battery is too low, apply power to it, and allow
-			 * it to charge if it connected, and it is critically
-			 * low.
+			 * it to charge if it is critically low.
 			 *
 			 * TODO(b:71881017): This will make the battery charge
 			 * oscillate between 3 and 4 percent, which might not be
 			 * great for battery life. We need some hysteresis.
 			 */
-			int base_current = db_policy.min_base_system_power;
+			/*
+			 * TODO(b:71881017): Precompute (ideally, at build time)
+			 * the base_current, so we do not need to do a division
+			 * here.
+			 */
+			int base_current =
+				(db_policy.min_base_system_power * 1000) /
+				db_policy.otg_voltage;
 			int lid_current = add_margin(base_current,
 						db_policy.margin_otg_current);