linux-kernel - Re: [PATCH v2] usb: typec: tcpm: Relax disconnect threshold during power negotiation

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Message-ID: <CAGZ6i=0RgyYJBvw7g+tGyFwBvBE-nV_WjpyZQ3HGToRgC-JhAQ@mail.gmail.com>
Date:   Wed, 16 Jun 2021 09:16:49 +0800
From:   Kyle Tso <kyletso@...gle.com>
To:     Badhri Jagan Sridharan <badhri@...gle.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: typec: tcpm: Relax disconnect threshold during
 power negotiation

On Wed, Jun 16, 2021 at 2:06 AM Badhri Jagan Sridharan
<badhri@...gle.com> wrote:
>
> On Tue, Jun 15, 2021 at 1:08 AM Kyle Tso <kyletso@...gle.com> wrote:
> >
> > If the voltage is being decreased in power negotiation, the Source will
> > set the power supply to operate at the new voltage level before sending
> > PS_RDY. For non-PPS negotiation, relax the disconnect threshold on Sink
> > after receiving Accept Message to ensure the relaxed setting is enabled
> > before the voltage collapse. For PPS, relax the threshold before
> > sending Request Message so that it will not race with Source which
> > begins to adjust the voltage right after it sends Accept Message.
> >
> > The real threshold will be set after Sink receives PS_RDY Message.
> >
> > Fixes: f321a02caebd ("usb: typec: tcpm: Implement enabling Auto Discharge disconnect support")
> > Cc: Badhri Jagan Sridharan <badhri@...gle.com>
> > Signed-off-by: Kyle Tso <kyletso@...gle.com>
> > ---
> > Changes since v1:
> > - move the timing of setting threshold up to "before sending Request"
> >   for PPS power negotiation so that it won't race with the Source.
> > - PPS: if it fails to send the Request, fallback to previous threshold
> > - PPS: if the Source doesn't respond Accept, fallback to previous
> >   threshold
> > - update the commit message for above changes
> >
> >  drivers/usb/typec/tcpm/tcpm.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> > index 0db685d5d9c0..00f3fd7c05d6 100644
> > --- a/drivers/usb/typec/tcpm/tcpm.c
> > +++ b/drivers/usb/typec/tcpm/tcpm.c
> > @@ -2599,6 +2599,11 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
> >                             port->send_discover)
> >                                 port->vdm_sm_running = true;
> >
> > +                       /* Threshold was relaxed before sending Request. Restore it back. */
> > +                       tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
> > +                                                              port->pps_data.active,
> > +                                                              port->supply_voltage);
> > +
> >                         tcpm_set_state(port, SNK_READY, 0);
> >                         break;
> >                 case DR_SWAP_SEND:
> > @@ -2646,6 +2651,8 @@ static void tcpm_pd_ctrl_request(struct tcpm_port *port,
> >                 switch (port->state) {
> >                 case SNK_NEGOTIATE_CAPABILITIES:
> >                         port->pps_data.active = false;
> > +                       /* Voltage is going to be at new level. Relax the threshold here. */
> > +                       tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, 0);
> >                         tcpm_set_state(port, SNK_TRANSITION_SINK, 0);
> >                         break;
> >                 case SNK_NEGOTIATE_PPS_CAPABILITIES:
> > @@ -3423,6 +3430,9 @@ static int tcpm_pd_send_pps_request(struct tcpm_port *port)
> >         if (ret < 0)
> >                 return ret;
> >
> > +       /* Relax the threshold as voltage will be adjusted right after Accept Message. */
> This makes sense. Shouldn't we have the same approach for
> tcpm_pd_send_request as it's equally applicable for fixed RDO as well
> ?
>

I don't think we need to do that because for the power negotiation
using Fixed RDO, the voltage adjustment from Source side takes place
after the time sending Accept Message plus tSrcTransition (25~35ms).
So setting the threshold after the Sink gets Accept Message should be
enough.

thanks,
Kyle

> > +       tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_USB, false, 0);
> > +
> >         memset(&msg, 0, sizeof(msg));
> >         msg.header = PD_HEADER_LE(PD_DATA_REQUEST,
> >                                   port->pwr_role,
> > @@ -4196,6 +4206,10 @@ static void run_state_machine(struct tcpm_port *port)
> >         case SNK_NEGOTIATE_PPS_CAPABILITIES:
> >                 ret = tcpm_pd_send_pps_request(port);
> >                 if (ret < 0) {
> > +                       /* Restore back to the original state */
> > +                       tcpm_set_auto_vbus_discharge_threshold(port, TYPEC_PWR_MODE_PD,
> > +                                                              port->pps_data.active,
> > +                                                              port->supply_voltage);
> >                         port->pps_status = ret;
> >                         /*
> >                          * If this was called due to updates to sink
> > --
> > 2.32.0.272.g935e593368-goog
> >