ln9310: Stronger workaround to prevent SCOUT overvoltage at startup

This improved workaround (compared to the previous 2520279) moves
the CFLY precharge step out of the ln9310's internal startup
sequence and implements it using I2C commands sent by the EC just before
the I2C command that triggers the ln9310 startup.  The workaround
additionally modifies the ln9310's internal startup sequence to use
the precharged CFLY capacitors as decoupling of an internal node
during the startup sequence which should help prevent an OV glitch
from appearing on the LN9310 output even if the internal level
shifter on SW1 glitches and pulls up on the C1PA/B nodes.

BRANCH=Trogdor
BUG=b:185308433
TEST=Should not break the current boot flow, i.e. power-up and
power-down (using long-press of the power button) should function
similar to before this change.  Testing the efficacy at preventing
the SCOUT overvoltage glitch must be done with LN9310 parts screened
out at wafer test that have a higher likelihood of exhibiting the
glitch at the SCOUT output.  With these parts, startup should be
observed with a scope probe monitoring LN9310 SCOUT for overvoltagee.

Change-Id: I216991f950196225cabbbfdaa2333f1650f7f4fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2837531
Reviewed-by: Alexandru M Stan <amstan@chromium.org>
Reviewed-by: Wai-Hong Tam <waihong@google.com>
Tested-by: John Crossley <crossley@lionsemi.corp-partner.google.com>
Commit-Queue: John Crossley <crossley@lionsemi.corp-partner.google.com>

1 files changed, 228 insertions, 23 deletions

diff --git a/driver/ln9310.c b/driver/ln9310.c
index 31c6dbca7a..d339c228a2 100644
--- a/driver/ln9310.c
+++ b/driver/ln9310.c
@@ -18,6 +18,7 @@
 #define CPRINTS(format, args...) cprints(CC_I2C, format, ## args)
 
 static int power_good;
+static int startup_workaround_required;
 
 int ln9310_power_good(void)
 {
@@ -119,22 +120,25 @@ static int ln9310_update_startup_seq(void)
 {
 	CPRINTS("LN9310 update startup sequence");
 
-	/* Startup sequence instruction swap */
+	/*
+	 * Startup sequence instruction swap to hold Cfly
+	 * bottom plate low during startup
+	 */
 	field_update8(LN9310_REG_LION_CTRL,
 		      LN9310_LION_CTRL_MASK,
-		      LN9310_LION_CTRL_UNLOCK);
+		      LN9310_LION_CTRL_UNLOCK_AND_EN_TM);
 
 	field_update8(LN9310_REG_SWAP_CTRL_0,
 		      0xff,
-		      0x3f);
+		      0x52);
 
 	field_update8(LN9310_REG_SWAP_CTRL_1,
 		      0xff,
-		      0x51);
+		      0x54);
 
 	field_update8(LN9310_REG_SWAP_CTRL_2,
 		      0xff,
-		      0x19);
+		      0xCC);
 
 	field_update8(LN9310_REG_SWAP_CTRL_3,
 		      0xff,
@@ -180,7 +184,7 @@ static int ln9310_init_3to1(void)
 		      LN9310_PWR_OP_MODE_MASK,
 		      LN9310_PWR_OP_MODE_SWITCH31);
 
-	/* 3S lower bounde delta configurations */
+	/* 3S lower bound delta configurations */
 	field_update8(LN9310_REG_LB_CTRL,
 		      LN9310_LB_DELTA_MASK,
 		      LN9310_LB_DELTA_3S);
@@ -217,7 +221,7 @@ static int ln9310_init_2to1(void)
 		      LN9310_PWR_OP_MODE_MASK,
 		      LN9310_PWR_OP_MODE_SWITCH21);
 
-	/* 2S lower bounde delta configurations */
+	/* 2S lower bound delta configurations */
 	field_update8(LN9310_REG_LB_CTRL,
 		      LN9310_LB_DELTA_MASK,
 		      LN9310_LB_DELTA_2S);
@@ -240,7 +244,7 @@ static int ln9310_update_infet(void)
 
 	field_update8(LN9310_REG_LION_CTRL,
 		      LN9310_LION_CTRL_MASK,
-		      LN9310_LION_CTRL_UNLOCK);
+		      LN9310_LION_CTRL_UNLOCK_AND_EN_TM);
 
 	/* Update Infet register settings */
 	field_update8(LN9310_REG_CFG_5,
@@ -268,11 +272,107 @@ static int ln9310_update_infet(void)
 	return EC_SUCCESS;
 }
 
+static int ln9310_precharge_cfly(uint64_t *precharge_timeout)
+{
+	int status = 0;
+	CPRINTS("LN9310 precharge cfly");
+
+	/* Unlock registers and enable test mode */
+	status |= field_update8(LN9310_REG_LION_CTRL,
+			LN9310_LION_CTRL_MASK,
+			LN9310_LION_CTRL_UNLOCK_AND_EN_TM);
+
+	/* disable test mode overrides */
+	status |= field_update8(LN9310_REG_FORCE_SC21_CTRL_2,
+			LN9310_FORCE_SC21_CTRL_2_FORCE_SW_CTRL_REQ_MASK,
+			LN9310_FORCE_SC21_CTRL_2_FORCE_SW_CTRL_REQ_OFF);
+
+	/* Configure test mode target values for precharge ckts.  */
+	status |= field_update8(LN9310_REG_FORCE_SC21_CTRL_1,
+			LN9310_FORCE_SC21_CTRL_1_TM_SC_OUT_CFLY_PRECHARGE_MASK,
+			LN9310_FORCE_SC21_CTRL_1_TM_SC_OUT_CFLY_PRECHARGE_ON);
+
+	/* Force SCOUT precharge/predischarge overrides */
+	status |= field_update8(LN9310_REG_TEST_MODE_CTRL,
+			LN9310_TEST_MODE_CTRL_FORCE_SC_OUT_PRECHARGE_MASK |
+			LN9310_TEST_MODE_CTRL_FORCE_SC_OUT_PREDISCHARGE_MASK,
+			LN9310_TEST_MODE_CTRL_FORCE_SC_OUT_PRECHARGE_ON |
+			LN9310_TEST_MODE_CTRL_FORCE_SC_OUT_PREDISCHARGE_ON);
+
+	/* Force enable CFLY precharge overrides */
+	status |= field_update8(LN9310_REG_FORCE_SC21_CTRL_2,
+			LN9310_FORCE_SC21_CTRL_2_FORCE_SW_CTRL_REQ_MASK,
+			LN9310_FORCE_SC21_CTRL_2_FORCE_SW_CTRL_REQ_ON);
+
+	/* delay long enough to ensure CFLY has time to fully precharge */
+	usleep(LN9310_CFLY_PRECHARGE_DELAY);
+
+	/* locking and leaving test mode will stop CFLY precharge */
+	*precharge_timeout = get_time().val + LN9310_CFLY_PRECHARGE_TIMEOUT;
+	status |= field_update8(LN9310_REG_LION_CTRL,
+			LN9310_LION_CTRL_MASK,
+			LN9310_LION_CTRL_LOCK);
+
+	return status;
+}
+
+static int ln9310_precharge_cfly_reset(void)
+{
+	int status = 0;
+	CPRINTS("LN9310 precharge cfly reset");
+
+	/* set known initial state for config bits related to cfly precharge */
+	status |= field_update8(LN9310_REG_LION_CTRL,
+		LN9310_LION_CTRL_MASK,
+		LN9310_LION_CTRL_UNLOCK);
+
+	/* Force off SCOUT precharge/predischarge overrides */
+	status |= field_update8(LN9310_REG_TEST_MODE_CTRL,
+			LN9310_TEST_MODE_CTRL_FORCE_SC_OUT_PRECHARGE_MASK |
+			LN9310_TEST_MODE_CTRL_FORCE_SC_OUT_PREDISCHARGE_MASK,
+			LN9310_TEST_MODE_CTRL_FORCE_SC_OUT_PRECHARGE_OFF |
+			LN9310_TEST_MODE_CTRL_FORCE_SC_OUT_PREDISCHARGE_OFF);
+
+	/* disable test mode overrides */
+	status |= field_update8(LN9310_REG_FORCE_SC21_CTRL_2,
+			LN9310_FORCE_SC21_CTRL_2_FORCE_SW_CTRL_REQ_MASK,
+			LN9310_FORCE_SC21_CTRL_2_FORCE_SW_CTRL_REQ_OFF);
+
+	/* disable CFLY and SC_OUT precharge control  */
+	status |= field_update8(LN9310_REG_FORCE_SC21_CTRL_1,
+			LN9310_FORCE_SC21_CTRL_1_TM_SC_OUT_CFLY_PRECHARGE_MASK,
+			LN9310_FORCE_SC21_CTRL_1_TM_SC_OUT_CFLY_PRECHARGE_OFF);
+
+	status |= field_update8(LN9310_REG_LION_CTRL,
+			LN9310_LION_CTRL_MASK,
+			LN9310_LION_CTRL_LOCK);
+
+	return status;
+}
+
 void ln9310_init(void)
 {
-	int status, val;
+	int status, val, chip_revision;
 	enum battery_cell_type batt;
 
+	/* Make sure initial state of LN9310 is STANDBY (i.e. output is off)  */
+	field_update8(LN9310_REG_STARTUP_CTRL,
+				LN9310_STARTUP_STANDBY_EN,
+				1);
+
+	/*
+	 * LN9310 software startup is only required for earlier silicon revs.
+	 * LN9310 hardware revisions after LN9310_BC_STS_C_CHIP_REV_FIXED
+	 * should not use the software startup sequence.
+	 */
+	status = raw_read8(LN9310_REG_BC_STS_C, &val);
+	if (status) {
+		CPRINTS("LN9310 reading BC_STS_C failed");
+		return;
+	}
+	chip_revision = val && LN9310_BC_STS_C_CHIP_REV_MASK;
+	startup_workaround_required = chip_revision < LN9310_BC_STS_C_CHIP_REV_FIXED;
+
 	/* Update INFET configuration  */
 	status = ln9310_update_infet();
 
@@ -312,11 +412,12 @@ void ln9310_init(void)
 	usleep(LN9310_CDC_DELAY);
 	CPRINTS("LN9310 OP_MODE Update method: Self-sync");
 
-	/* Update Startup sequence */
-	status = ln9310_update_startup_seq();
-
-	if (status != EC_SUCCESS)
-		return;
+	if (startup_workaround_required) {
+		/* Update Startup sequence */
+		status = ln9310_update_startup_seq();
+		if (status != EC_SUCCESS)
+			return;
+	}
 
 	batt = board_get_battery_cell_type();
 	if (batt == BATTERY_CELL_TYPE_3S) {
@@ -333,20 +434,124 @@ void ln9310_init(void)
 
 	/* Unmask the MODE change interrupt */
 	field_update8(LN9310_REG_INT1_MSK,
-		      LN9310_INT1_MODE,
-		      0);
+			LN9310_INT1_MODE,
+			0);
+}
 
+void ln9310_software_enable(int enable)
+{
+	int status, val, retry_count;
+	uint64_t precharge_timeout;
+	bool ln9310_init_completed = false;
+
+	/*
+	 * LN9310 startup requires (nEN=0 AND STANDBY_EN=0) where nEN is a pin
+	 * and STANDBY_EN is a register bit. Previous EC firmware set
+	 * STANDBY_EN=1 in ln9310_init and toggled nEN to startup/shutdown. This
+	 * function implements an alternate software (i.e. controlled by EC
+	 * through I2C commands) startup sequence so one option is to set nEN=1
+	 * and just used ln9310_software_enable to startup/shutdown.
+	 * ln9310_software_enable can also be used in conjunction w/ the nEN pin
+	 * (in case nEN pin is desired as visible signal ) as follows:
+	 *
+	 * Initial battery insertion:
+	 * nEN=1
+	 * ln9310_init() - initial condition is STANDBY_EN=1
+	 *
+	 * Power up LN9310:
+	 * nEN=0 - STANDBY_EN should be 1 so this doesn't trigger startup
+	 * ln9310_software_enable(1) - triggers alternate software-based startup
+	 *
+	 * Power down LN9310:
+	 * nEN=1 - shutdown LN9310 (shutdown seq. does not require modification)
+	 * ln9310_software_enable(0) - reset LN9310 register to state necessary
+	 *                             for subsequent startups
+	 */
 	/* Dummy clear all interrupts */
 	status = raw_read8(LN9310_REG_INT1, &val);
 	if (status) {
 		CPRINTS("LN9310 reading INT1 failed");
 		return;
 	}
-
-	/* Clear the STANDBY_EN bit */
-	field_update8(LN9310_REG_STARTUP_CTRL,
-		      LN9310_STARTUP_STANDBY_EN,
-		      0);
-
 	CPRINTS("LN9310 cleared interrupts: 0x%x", val);
-}
+
+	if (startup_workaround_required) {
+		if (enable) {
+			/*
+			* Software modification of LN9310 startup sequence w/ retry
+			* loop.
+			*
+			* (1) Clear interrupts
+			* (2) Precharge Cfly w/ overrides of internal LN9310 signals
+			* (3) disable overrides -> stop precharging Cfly
+			* (4.1) if < 100 ms elapsed since (2) -> trigger LN9310 internal
+			*                                        startup seq. 
+			* (4.2) else -> abort and optionally retry from step 2
+			*/
+			retry_count = 0;
+			while (!ln9310_init_completed && retry_count < LN9310_INIT_RETRY_COUNT) {
+				/* Precharge CFLY before starting up */
+				status = ln9310_precharge_cfly(&precharge_timeout);
+				if (status != EC_SUCCESS) {
+					CPRINTS("LN9310 failed to run Cfly precharge sequence");
+					status = ln9310_precharge_cfly_reset();
+					retry_count++;
+					continue;
+				}
+
+				/*
+				* Only start the SC if the cfly precharge
+				* hasn't timed out (i.e. ended too long ago)
+				*/
+				if (get_time().val < precharge_timeout) {
+					/* Clear the STANDBY_EN bit to enable the SC */
+					field_update8(LN9310_REG_STARTUP_CTRL,
+							LN9310_STARTUP_STANDBY_EN,
+							0);
+					if (get_time().val > precharge_timeout ) {
+						/*
+						* if timed out during previous I2C command, abort 
+						* startup attempt
+						*/
+						field_update8(LN9310_REG_STARTUP_CTRL,
+							LN9310_STARTUP_STANDBY_EN,
+							1);
+					} else {
+						/* all other paths should reattempt startup  */
+						ln9310_init_completed = true;
+					}
+				}
+				/* Reset to known state for config bits related to cfly precharge */
+				ln9310_precharge_cfly_reset();
+				retry_count++;
+			}
+
+			if (!ln9310_init_completed) {
+				CPRINTS("LN9310 failed to start after %d retry attempts",
+						retry_count);
+			}
+		} else {
+			/*
+			* Internal LN9310 shutdown sequence is ok as is, so just reset
+			* the state to prepare for subsequent startup sequences.
+			*
+			* (1) set STANDBY_EN=1 to be sure the part turns off even if nEN=0
+			* (2) reset cfly precharge related registers to known initial state
+			*/
+			field_update8(LN9310_REG_STARTUP_CTRL,
+					LN9310_STARTUP_STANDBY_EN,
+					1);
+
+			ln9310_precharge_cfly_reset();
+		}
+	} else {
+		/*
+		* for newer LN9310 revsisions, the startup workaround is not required
+		* so the STANDBY_EN bit can just be set directly
+		*/
+		field_update8(LN9310_REG_STARTUP_CTRL,
+					LN9310_STARTUP_STANDBY_EN,
+					!enable);
+	}
+	return;
+}
\ No newline at end of file