op-pwrctl: Make latch transparent briefly, only after state changes

The Zaius motherboard has latches between BMC control pins to power up
the host and the input pins to the power sequencer. This allows BMC
resets to not interrupt power to the host.

Currently, the latches are made transparent prior to sampling the power
state of the system, which causes BMC boot to kill host power. In
addition the latches remain transparent, so the system can be brought
down by the BMC shutting down.

Enable the latches only after power control pins change state.
Enable the latches only momentarily.

After this change, Zaius BMC can reboot without taking down its host.

Signed-off-by: Xo Wang <xow@google.com>
Change-Id: If150cbcf3fabda359d1ce94602c40cb96741e869

1 files changed, 36 insertions, 25 deletions

diff --git a/op-pwrctl/power_control_obj.c b/op-pwrctl/power_control_obj.c
index bd0287a..60c9009 100644
--- a/op-pwrctl/power_control_obj.c
+++ b/op-pwrctl/power_control_obj.c
@@ -220,6 +220,7 @@ on_set_power_state(ControlPower *pwr,
 		gpointer user_data)
 {
 	Control* control = object_get_control((Object*)user_data);
+	PowerGpio *power_gpio = &g_gpio_configs.power_gpio;
 	if(state > 1)
 	{
 		g_dbus_method_invocation_return_dbus_error(invocation,
@@ -244,17 +245,17 @@ on_set_power_state(ControlPower *pwr,
 			} else {
 				control_emit_goto_system_state(control,"HOST_POWERING_OFF");
 			}
-			for (i = 0; i < g_gpio_configs.power_gpio.num_power_up_outs; i++) {
-				GPIO *power_pin = &g_gpio_configs.power_gpio.power_up_outs[i];
+			for (i = 0; i < power_gpio->num_power_up_outs; i++) {
+				GPIO *power_pin = &power_gpio->power_up_outs[i];
 				error = gpio_open(power_pin);
 				if(error != GPIO_OK) {
 					g_print("ERROR PowerControl: GPIO open error (gpio=%s,rc=%d)\n",
-							g_gpio_configs.power_gpio.power_up_outs[i].name, error);
+							power_gpio->power_up_outs[i].name, error);
 					continue;
 				}
-				power_up_out = state ^ !g_gpio_configs.power_gpio.power_up_pols[i];
+				power_up_out = state ^ !power_gpio->power_up_pols[i];
 				g_print("PowerControl: setting power up %s to %d\n",
-						g_gpio_configs.power_gpio.power_up_outs[i].name, (int)power_up_out);
+						power_gpio->power_up_outs[i].name, (int)power_up_out);
 				error = gpio_write(power_pin, power_up_out);
 				if(error != GPIO_OK) {
 					continue;
@@ -268,7 +269,37 @@ on_set_power_state(ControlPower *pwr,
 		{
 			g_print("ERROR PowerControl: GPIO set power state (rc=%d)\n",error);
 		}
+
+		/* If there's a latch, it should be enabled following changes to the
+		 * power pins' states. This commits the changes to the latch states. */
+		if (power_gpio->latch_out.name != NULL) {
+			int rc;
+			uint8_t latch_value = 0;
+			rc = gpio_open(&power_gpio->latch_out);
+			if (rc != GPIO_OK) {
+				/* Failures are non-fatal. */
+				g_print("PowerControl ERROR failed to open latch %s rc=%d\n",
+						power_gpio->latch_out.name, rc);
+				return TRUE;
+			}
+			/* Make the latch transparent for as brief of a time as possible. */
+			rc = gpio_write(&power_gpio->latch_out, 1);
+			if (rc != GPIO_OK) {
+				g_print("PowerControl ERROR failed to assert latch %s rc=%d\n",
+						power_gpio->latch_out.name, rc);
+			} else {
+				g_print("PowerControl asserted latch %s\n",
+						power_gpio->latch_out.name);
+			}
+			rc = gpio_write(&power_gpio->latch_out, 0);
+			if (rc != GPIO_OK) {
+				g_print("PowerControl ERROR failed to clear latch %s rc=%d\n",
+						power_gpio->latch_out.name, rc);
+			}
+			gpio_close(&power_gpio->latch_out);
+		}
 	}
+
 	return TRUE;
 }
 
@@ -334,26 +365,6 @@ set_up_gpio(GDBusConnection *connection,
 		}
 	}
 
-	/* If there's a latch, it only needs to be set once. */
-	if(power_gpio->latch_out.name != NULL) {
-		do {
-			rc = gpio_open(&power_gpio->latch_out);
-			if(rc != GPIO_OK) {
-				/* Failures are non-fatal. */
-				break;
-			}
-			rc = gpio_write(&power_gpio->latch_out, 1);
-			gpio_close(&power_gpio->latch_out);
-		} while(0);
-		if (rc != GPIO_OK) {
-			error = rc;
-			g_print("PowerControl ERROR failed to assert latch %s rc=%d\n",
-					power_gpio->latch_out.name, rc);
-		} else {
-			g_print("PowerControl asserted latch %s\n", power_gpio->latch_out.name);
-		}
-	}
-
 	rc = gpio_open(&power_gpio->power_good_in);
 	if(rc != GPIO_OK) {
 		return rc;