linux-kernel - [PATCH] usb: typec: fusb302: cache PD RX state

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Message-Id: <20250704-fusb302-race-condition-fix-v1-1-239012c0e27a@kernel.org>
Date: Fri, 04 Jul 2025 19:55:06 +0200
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Heikki Krogerus <heikki.krogerus@...ux.intel.com>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Guenter Roeck <linux@...ck-us.net>, Yueyao Zhu <yueyao@...gle.com>
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, 
 kernel@...labora.com, stable@...r.kernel.org, 
 Sebastian Reichel <sebastian.reichel@...labora.com>
Subject: [PATCH] usb: typec: fusb302: cache PD RX state

This patch fixes a race condition communication error, which ends up in
PD hard resets when losing the race. Some systems, like the Radxa ROCK
5B are powered through USB-C without any backup power source and use a
FUSB302 chip to do the PD negotiation. This means it is quite important
to avoid hard resets, since that effectively kills the system's
power-supply.

I've found the following race condition while debugging unplanned power
loss during booting the board every now and then:

1. lots of TCPM/FUSB302/PD initialization stuff
2. TCPM ends up in SNK_WAIT_CAPABILITIES (tcpm_set_pd_rx is enabled here)
3. the remote PD source does not send anything, so TCPM does a SOFT RESET
4. TCPM ends up in SNK_WAIT_CAPABILITIES for the second time
   (tcpm_set_pd_rx is enabled again, even though it is still on)

At this point I've seen broken CRC good messages being send by the
FUSB302 with a logic analyzer sniffing the CC lines. Also it looks like
messages are being lost and things generally going haywire with one of
the two sides doing a hard reset once a broken CRC good message was send
to the bus.

I think the system is running into a race condition, that the FIFOs are
being cleared and/or the automatic good CRC message generation flag is
being updated while a message is already arriving.

Let's avoid this by caching the PD RX enabled state, as we have already
processed anything in the FIFOs and are in a good state. As a side
effect that this also optimizes I2C bus usage :)

As far as I can tell the problem theoretically also exists when TCPM
enters SNK_WAIT_CAPABILITIES the first time, but I believe this is less
critical for the following reason:

On devices like the ROCK 5B, which are powered through a TCPM backed
USB-C port, the bootloader must have done some prior PD communication
(initial communication must happen within 5 seconds after plugging the
USB-C plug). This means the first time the kernel TCPM state machine
reaches SNK_WAIT_CAPABILITIES, the remote side is not sending messages
actively. On other devices a hard reset simply adds some extra delay and
things should be good afterwards.

Fixes: c034a43e72dda ("staging: typec: Fairchild FUSB302 Type-c chip driver")
Cc: stable@...r.kernel.org
Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.com>
---
 drivers/usb/typec/tcpm/fusb302.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/usb/typec/tcpm/fusb302.c b/drivers/usb/typec/tcpm/fusb302.c
index f15c63d3a8f441569ec98302f5b241430d8e4547..870a71f953f6cd8dfc618caea56f72782e40ee1c 100644
--- a/drivers/usb/typec/tcpm/fusb302.c
+++ b/drivers/usb/typec/tcpm/fusb302.c
@@ -104,6 +104,7 @@ struct fusb302_chip {
 	bool vconn_on;
 	bool vbus_on;
 	bool charge_on;
+	bool pd_rx_on;
 	bool vbus_present;
 	enum typec_cc_polarity cc_polarity;
 	enum typec_cc_status cc1;
@@ -841,6 +842,11 @@ static int tcpm_set_pd_rx(struct tcpc_dev *dev, bool on)
 	int ret = 0;

 	mutex_lock(&chip->lock);
+	if (chip->pd_rx_on == on) {
+		fusb302_log(chip, "pd is already %s", str_on_off(on));
+		goto done;
+	}
+
 	ret = fusb302_pd_rx_flush(chip);
 	if (ret < 0) {
 		fusb302_log(chip, "cannot flush pd rx buffer, ret=%d", ret);
@@ -863,6 +869,8 @@ static int tcpm_set_pd_rx(struct tcpc_dev *dev, bool on)
 			    str_on_off(on), ret);
 		goto done;
 	}
+
+	chip->pd_rx_on = on;
 	fusb302_log(chip, "pd := %s", str_on_off(on));
 done:
 	mutex_unlock(&chip->lock);

---
base-commit: c435a4f487e8c6a3b23dafbda87d971d4fd14e0b
change-id: 20250704-fusb302-race-condition-fix-9cc9de73f05d

Best regards,
-- 
Sebastian Reichel <sre@...nel.org>