usb: typec: tcpm: Wait for vbus discharge to VSAFE0V before toggling

usb: typec: tcpm: Wait for vbus discharge to VSAFE0V before toggling

When vbus auto discharge is enabled, TCPM can sometimes be faster than
the TCPC i.e. TCPM can go ahead and move the port to unattached state
(involves disabling vbus auto discharge) before TCPC could effectively
discharge vbus to VSAFE0V. This leaves vbus with residual charge and
increases the decay time which prevents tsafe0v from being met.
This change makes TCPM waits for a maximum of tSafe0V(max) for vbus
to discharge to VSAFE0V before transitioning to unattached state
and re-enable toggling. If vbus discharges to vsafe0v sooner, then,
transition to unattached state
happens right away.

Also, while in SNK_READY, when auto discharge is enabled, drive
disconnect based on vbus turning off instead of Rp disappearing on
CC pins. Rp disappearing on CC pins is almost instanteous compared
to vbus decay.

Sink detach:
[  541.703058] CC1: 3 -> 0, CC2: 0 -> 0 [state SNK_READY, polarity 0, disconnected]
[  541.703331] Setting voltage/current limit 5000 mV 0 mA
[  541.727235] VBUS on
[  541.749650] VBUS off
[  541.749653] pending state change SNK_READY -> SNK_UNATTACHED @ 650 ms [rev3 NONE_AMS]
[  541.749944] VBUS VSAFE0V
[  541.749945] state change SNK_READY -> SNK_UNATTACHED [rev3 NONE_AMS]
[  541.750806] Disable vbus discharge ret:0
[  541.907345] Start toggling
[  541.922799] CC1: 0 -> 0, CC2: 0 -> 0 [state TOGGLING, polarity 0, disconnected]

Source detach:
[ 2555.310414] state change SRC_SEND_CAPABILITIES -> SRC_READY [rev3 POWER_NEGOTIATION]
[ 2555.310675] AMS POWER_NEGOTIATION finished
[ 2555.310679] cc:=3
[ 2593.645886] CC1: 0 -> 0, CC2: 2 -> 0 [state SRC_READY, polarity 1, disconnected]
[ 2593.645919] pending state change SRC_READY -> SNK_UNATTACHED @ 650 ms [rev3 NONE_AMS]
[ 2593.648419] VBUS off
[ 2593.648960] VBUS VSAFE0V
[ 2593.648965] state change SRC_READY -> SNK_UNATTACHED [rev3 NONE_AMS]
[ 2593.649962] Disable vbus discharge ret:0
[ 2593.890322] Start toggling
[ 2593.925663] CC1: 0 -> 0, CC2: 0 -> 0 [state TOGGLING, polarity 0,

Fixes: f321a02caebd ("usb: typec: tcpm: Implement enabling Auto Discharge disconnect support")
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Link: https://lore.kernel.org/r/20210225101104.1680697-1-badhri@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>