linux-kernel - Re: [PATCH v1] usb: typec: tcpm: Wait for vbus discharge to VSAFE0V before toggling

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Message-ID: <CAPTae5+qhE9uo2s20oEQd0x+nW21zGE3S7QWkR=oqqVX-3uHmg@mail.gmail.com>
Date:   Thu, 18 Feb 2021 02:38:45 -0800
From:   Badhri Jagan Sridharan <badhri@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Kyle Tso <kyletso@...gle.com>, USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] usb: typec: tcpm: Wait for vbus discharge to VSAFE0V
 before toggling

Hi Greg,

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

commit f321a02caebdd0c56e167610cda2fa148cd96e8b
Author: Badhri Jagan Sridharan <badhri@...gle.com>
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 <badhri@...gle.com>
    Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
    Link: https://lore.kernel.org/r/20201029063138.1429760-8-badhri@google.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Thanks,
Badhri

On Thu, Feb 18, 2021 at 2:10 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Thu, Feb 18, 2021 at 02:02:43AM -0800, Badhri Jagan Sridharan wrote:
> > 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@...gle.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