[PATCH v3 1/2] usb: typec: tcpm: Do not disconnect while receiving VBUS off

[Badhri Jagan Sridharan <badhri@google.com>]

With some chargers, vbus might momentarily raise above VSAFE5V and fall
back to 0V before tcpm gets to read port->tcpc->get_vbus. This will
report a VBUS off event causing TCPM to transition to SNK_UNATTACHED
where it should be waiting in either SNK_ATTACH_WAIT or SNK_DEBOUNCED
state. This patch makes TCPM avoid vbus off events while in
SNK_ATTACH_WAIT or SNK_DEBOUNCED state.

Stub from the spec:
    "4.5.2.2.4.2 Exiting from AttachWait.SNK State
    A Sink shall transition to Unattached.SNK when the state of both
    the CC1 and CC2 pins is SNK.Open for at least tPDDebounce.
    A DRP shall transition to Unattached.SRC when the state of both
    the CC1 and CC2 pins is SNK.Open for at least tPDDebounce."

[23.194131] CC1: 0 -> 0, CC2: 0 -> 5 [state SNK_UNATTACHED, polarity 0, connected]
[23.201777] state change SNK_UNATTACHED -> SNK_ATTACH_WAIT [rev3 NONE_AMS]
[23.209949] pending state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED @ 170 ms [rev3 NONE_AMS]
[23.300579] VBUS off
[23.300668] state change SNK_ATTACH_WAIT -> SNK_UNATTACHED [rev3 NONE_AMS]
[23.301014] VBUS VSAFE0V
[23.301111] Start toggling

Fixes: f0690a25a140b8 ("staging: typec: USB Type-C Port Manager (tcpm)")
Cc: stable@vger.kernel.org
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
---
Changes since v1:
- Fix typos stated by Guenter Roeck.
Changes since v2:
- Added reviewed/acked-by tags
---
 drivers/usb/typec/tcpm/tcpm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 59d4fa2443f2..3bf79f52bd34 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -5156,7 +5156,8 @@ static void _tcpm_pd_vbus_off(struct tcpm_port *port)
 	case SNK_TRYWAIT_DEBOUNCE:
 		break;
 	case SNK_ATTACH_WAIT:
-		tcpm_set_state(port, SNK_UNATTACHED, 0);
+	case SNK_DEBOUNCED:
+		/* Do nothing, as TCPM is still waiting for vbus to reach VSAFE5V to connect */
 		break;
 
 	case SNK_NEGOTIATE_CAPABILITIES:
-- 
2.35.0.rc0.227.g00780c9af4-goog