Hi Greg,

This patch is a bug fix for the following patch which was introduced in 5.11.

commit f321a02caebdd0c56e167610cda2fa148cd96e8b
Author: Badhri Jagan Sridharan [off-list ref]
Date:   Wed Oct 28 23:31:35 2020 -0700

    usb: typec: tcpm: Implement enabling Auto Discharge disconnect support

    TCPCI spec allows TCPC hardware to autonomously discharge the vbus
    capacitance upon disconnect. The expectation is that the TCPM enables
    AutoDischargeDisconnect while entering SNK/SRC_ATTACHED states. Hardware
    then automously discharges vbus when the vbus falls below a certain
    threshold i.e. VBUS_SINK_DISCONNECT_THRESHOLD.

    Apart from enabling the vbus discharge circuit, AutoDischargeDisconnect
    is also used a flag to move TCPCI based TCPC implementations into
    Attached.Snk/Attached.Src state as mentioned in
    Figure 4-15. TCPC State Diagram before a Connection of the
    USB Type-C Port Controller Interface Specification.
    In such TCPC implementations, setting AutoDischargeDisconnect would
    prevent TCPC into entering "Connection_Invalid" state as well.

    Signed-off-by: Badhri Jagan Sridharan [off-list ref]
    Reviewed-by: Heikki Krogerus [off-list ref]
    Link: https://lore.kernel.org/r/20201029063138.1429760-8-badhri@google.com (local)
    Signed-off-by: Greg Kroah-Hartman [off-list ref]

Thanks,
Badhri

On Thu, Feb 18, 2021 at 2:10 AM Greg Kroah-Hartman
[off-list ref] wrote:

On Thu, Feb 18, 2021 at 02:02:43AM -0800, Badhri Jagan Sridharan wrote:

quoted

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 introduces a new state VBUS_DISCHARGE where the 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.

Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
---
 drivers/usb/typec/tcpm/tcpm.c | 60 +++++++++++++++++++++++++++++++----
 1 file changed, 53 insertions(+), 7 deletions(-)

As this seems to be a bugfix, what commit does it fix?  Should it go to
stable kernels?  If so, how far back?

And as this is the merge window, I can't do anything with this until
5.12-rc1 is out, so be prepared for the delay...

thanks,

greg k-h