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@vger.kernel.org Signed-off-by: Sebastian Reichel sebastian.reichel@collabora.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,