charger: bd99955: Adjust VSYS based on fast vs precharge state

Rohm suggests setting VSYS to the higher value during precharge and only
setting it to the lower voltage after we have crossed the lower voltage.
Note that the VSYS register also controls the pre vs fastcharge
threshold, so setting VSYS to the lower voltage essentially enables
fastcharge.

BUG=chrome-os-partner:55524
BRANCH=None
TEST=Manual on kevin, verify dead battery is able to charge through
precharge to fastcharge.

Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Change-Id: Ia5b953c8dfbb25970ab329d5487a317ad37ba609
Reviewed-on: https://chromium-review.googlesource.com/362442
Commit-Ready: Shawn N <shawnn@chromium.org>
Tested-by: David Schneider <dnschneid@chromium.org>
Reviewed-by: Vijay P Hiremath <vijay.p.hiremath@intel.com>
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>

2 files changed, 109 insertions, 10 deletions

diff --git a/driver/charger/bd99955.c b/driver/charger/bd99955.c
index 11217428e5..260eba8945 100644
--- a/driver/charger/bd99955.c
+++ b/driver/charger/bd99955.c
@@ -553,19 +553,113 @@ int charger_get_status(int *status)
 	return EC_SUCCESS;
 }
 
-int charger_set_mode(int mode)
+/*
+ * Track charging state and update VSYS / charge enable when needed.
+ * VSYS must be set to FASTCHARGE_VSYSREG when charging in fastcharge mode,
+ * and PRECHARGE_DISCHARGE_VSYSREG otherwise.
+ */
+enum bd99955_charge_update {
+	BD99955_UPDATE_STOP_CHARGING,
+	BD99955_UPDATE_START_CHARGING,
+	BD99955_UPDATE_BAT_VOLTAGE,
+};
+
+enum bd99955_charge_state {
+	BD99955_CHARGE_STATE_UNINITIALIZED,
+	BD99955_CHARGE_STATE_NOT_CHARGING,
+	BD99955_CHARGE_STATE_PRECHARGE,
+	BD99955_CHARGE_STATE_FASTCHARGE,
+};
+
+/*
+ * Update battery charge state of bd99955 based upon parameter which indicates
+ * type of change.
+ */
+static int bd99955_update_charge_state(enum bd99955_charge_update update)
 {
+	static enum bd99955_charge_state charge_state =
+		BD99955_CHARGE_STATE_UNINITIALIZED;
+	enum bd99955_charge_state new_state;
 	int rv;
+	int bat_voltage = 0;
+
+	switch (update) {
+	case BD99955_UPDATE_STOP_CHARGING:
+		/* Transition directly to not charging state if asked */
+		new_state = BD99955_CHARGE_STATE_NOT_CHARGING;
+		break;
+	case BD99955_UPDATE_BAT_VOLTAGE:
+		/* Battery voltage change is irrelevant if we're not charging */
+		if (charge_state == BD99955_CHARGE_STATE_NOT_CHARGING) {
+			new_state = BD99955_CHARGE_STATE_NOT_CHARGING;
+			break;
+		}
+		/* Fall through */
+	case BD99955_UPDATE_START_CHARGING:
+		/* Transition to fast or precharge upon battery */
+		rv = ch_raw_read16(BD99955_CMD_VBAT_VAL, &bat_voltage,
+				   BD99955_EXTENDED_COMMAND);
+
+		/* Assume we're in precharge range on read error */
+		if (rv)
+			bat_voltage = 0;
+		new_state = bat_voltage > FASTCHARGE_VSYSREG ?
+			BD99955_CHARGE_STATE_FASTCHARGE :
+			BD99955_CHARGE_STATE_PRECHARGE;
+		break;
+	default:
+		panic("Invalid update param");
+	}
+
+	if (new_state == charge_state)
+		return 0;
 
-	if (mode & CHARGE_FLAG_INHIBIT_CHARGE) {
-		rv = bd99955_set_vsysreg(DISCHARGE_VSYSREG);
-		msleep(50);
+	CPRINTS("New bd99955 state: %d (%d mV)", new_state, bat_voltage);
+
+	switch (new_state) {
+	case BD99955_CHARGE_STATE_NOT_CHARGING:
+		/* Bring up vsys if necessary, then disable charging */
+		if (charge_state != BD99955_CHARGE_STATE_PRECHARGE) {
+			rv = bd99955_set_vsysreg(PRECHARGE_DISCHARGE_VSYSREG);
+			msleep(50);
+		}
 		rv |= bd99955_charger_enable(0);
-	} else {
-		rv = bd99955_charger_enable(1);
-		msleep(1);
-		rv |= bd99955_set_vsysreg(CHARGE_VSYSREG);
+		break;
+
+	case BD99955_CHARGE_STATE_PRECHARGE:
+	case BD99955_CHARGE_STATE_FASTCHARGE:
+		/*
+		 * Enable charging if necessary, then bring down vsys if
+		 * fastcharging.
+		 */
+		if (charge_state != BD99955_CHARGE_STATE_PRECHARGE &&
+		    charge_state != BD99955_CHARGE_STATE_FASTCHARGE) {
+			rv = bd99955_charger_enable(1);
+			msleep(1);
+		}
+		rv |= bd99955_set_vsysreg(
+			new_state == BD99955_CHARGE_STATE_PRECHARGE ?
+				     PRECHARGE_DISCHARGE_VSYSREG :
+				     FASTCHARGE_VSYSREG);
+		break;
+
+	default:
+		panic("Invalid bd99955 state");
 	}
+
+	charge_state = new_state;
+	return rv;
+}
+
+int charger_set_mode(int mode)
+{
+	int rv;
+
+	if (mode & CHARGE_FLAG_INHIBIT_CHARGE)
+		rv = bd99955_update_charge_state(BD99955_UPDATE_STOP_CHARGING);
+	else
+		rv = bd99955_update_charge_state(BD99955_UPDATE_START_CHARGING);
+
 	if (rv)
 		return rv;
 
@@ -594,6 +688,9 @@ int charger_set_current(int current)
 {
 	int rv;
 
+	/* Switch between precharge and fastcharge if required */
+	bd99955_update_charge_state(BD99955_UPDATE_BAT_VOLTAGE);
+
 	/* Charge current step 64 mA */
 	current &= ~0x3F;
 
diff --git a/driver/charger/bd99955.h b/driver/charger/bd99955.h
index 214a20fd7b..a2b53bbbae 100644
--- a/driver/charger/bd99955.h
+++ b/driver/charger/bd99955.h
@@ -43,8 +43,10 @@ enum bd99955_charge_port {
 #define BD99955_NO_BATTERY_CHARGE_I_MIN	512
 
 /* VSYSREG settings */
-#define DISCHARGE_VSYSREG	8960
-#define CHARGE_VSYSREG		6144
+/* Setting for precharge charging and discharge */
+#define PRECHARGE_DISCHARGE_VSYSREG	8960
+/* Setting for fastcharge charging */
+#define FASTCHARGE_VSYSREG		6144
 
 /* Battery Charger Commands */
 #define BD99955_CMD_CHG_CURRENT		0x14