control UART_EC RX/TX based on EC-CR50 communication status

This patch allows EC-CR50 communication to enable EC UART only
if EC is on and bitbang mode is disabled. EC UART shall be enabled
even when CCD_CAP_GSC_TX_EC_RX is disabled, EC UART is ccdblocked,
or servo is connected. EC-CR50 comm supporting boards are supposed
to have H1 dominate EC UART TX line against servo.

Servo detection, which is checked every second, shall be delayed
during EC-CR50 communication because EC UART TX pin
(GPIO_SERVO_DETECT) is used as an output. Servo state shall be
held as it was. Once EC-CR50 communication is done, the servo
detection will resume or CCD state gets updated based on what
it used to be before EC-CR50 communication.

BUG=chromium:1035706
BRANCH=cr50
TEST=manually tested on a reworked Helios.

// CCD connection only
> ccdstate
AP:      off
AP UART: off
EC:      on
Rdd:     connected
Servo:   undetectable
CCD EXT: enabled
State flags: UARTEC+TX I2C SPI
CCD ports blocked: (none)
> ecrst pulse
Pulsing EC reset
EC_RST_L is deasserted

// Servo connection only
> ccdstate
AP:      off
AP UART: off
EC:      on
Rdd:     disconnected
Servo:   connected
CCD EXT: disabled
State flags: I2C
CCD ports blocked: (none)

Change-Id: I02667bee004d237d846393a18f247970982c71b7
Signed-off-by: Namyoon Woo <namyoon@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2023239
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>

2 files changed, 37 insertions, 3 deletions

diff --git a/board/cr50/rdd.c b/board/cr50/rdd.c
index 9cc217129c..7a4b2de8d3 100644
--- a/board/cr50/rdd.c
+++ b/board/cr50/rdd.c
@@ -222,11 +222,18 @@ static void ccd_state_change_hook(void)
 
 	/* Start out by figuring what flags we might want enabled */
 
-	/* Enable EC/AP UART RX if that device is on */
+	/* Enable AP UART RX if that device is on */
 	if (ap_uart_is_on())
 		flags_want |= CCD_ENABLE_UART_AP;
-	if (ec_is_rx_allowed())
-		flags_want |= CCD_ENABLE_UART_EC;
+	/*
+	 * Enable EC UART RX.
+	 * Checking that EC is off (ec_is_rx_allowed()) will be done in the end,
+	 * and CCD_ENABLE_UART_EC will be cleared if so. This is to guarantee
+	 * that EC UART RX won't be enabled if EC is off even with any codes
+	 * overriding this flag. We also intend to keep ec_is_rx_allowed()
+	 * called once.
+	 */
+	flags_want |= CCD_ENABLE_UART_EC;
 
 #ifdef CONFIG_UART_BITBANG
 	if (uart_bitbang_is_wanted())
@@ -289,6 +296,21 @@ static void ccd_state_change_hook(void)
 	if (ccd_block & CCD_BLOCK_EC_UART)
 		flags_want &= ~CCD_ENABLE_UART_EC;
 
+	/*
+	 * EC UART flags are cleared if ccd ext is not detected or if ccd block
+	 * EC UART is enabled. EC-CR50 comm trumps both of those conditions.
+	 * Re-enable the EC UART flags if EC-CR50 comm is enabled.
+	 */
+	if (ec_comm_is_uart_in_packet_mode(UART_EC))
+		flags_want |= (CCD_ENABLE_UART_EC | CCD_ENABLE_UART_EC_TX);
+
+	/*
+	 * Disable EC UART RX if that device is off, otherwise there will be
+	 * an UART interrupt storm.
+	 */
+	if (!ec_is_rx_allowed())
+		flags_want &= ~CCD_ENABLE_UART_EC;
+
 	/* UARTs are either RX-only or RX+TX, so no RX implies no TX */
 	if (!(flags_want & CCD_ENABLE_UART_AP))
 		flags_want &= ~CCD_ENABLE_UART_AP_TX;
diff --git a/board/cr50/servo_state.c b/board/cr50/servo_state.c
index f6ded01dd0..5c05d2bb77 100644
--- a/board/cr50/servo_state.c
+++ b/board/cr50/servo_state.c
@@ -146,6 +146,18 @@ static void servo_detect(void)
 	if (state == DEVICE_STATE_IGNORED)
 		return;
 
+	/*
+	 * During EC-CR50 communication, do not change servo state because
+	 * GPIO_DETECT_SERVO (DIOB5) is not available. Return now, and
+	 * let it try to detect in the next second.
+	 *
+	 * Note: Though servo is not detectable, we do not want to change
+	 *       servo_state as UNDETECTABLE, otherwise "servo_is_connected()"
+	 *       might return false while servo is connected.
+	 */
+	if (ec_comm_is_uart_in_packet_mode(UART_EC))
+		return;
+
 	/* If we're driving EC UART TX, we can't detect servo */
 	if (!servo_detectable()) {
 		/* We're driving one port; might as well drive them all */