linux-kernel - Re: [PATCH v2] usb: typec: tcpm: collision avoidance

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Message-ID: <CAGZ6i=10-DVWRseYXjRGVyRtnTijT9Mg_TBTkv=3qWiMfv28cw@mail.gmail.com>
Date:   Thu, 19 Sep 2019 18:48:32 +0800
From:   Kyle Tso <kyletso@...gle.com>
To:     Adam Thomson <Adam.Thomson.Opensource@...semi.com>
Cc:     Hans de Goede <hdegoede@...hat.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Greg KH <gregkh@...uxfoundation.org>,
        Badhri Jagan Sridharan <badhri@...gle.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: typec: tcpm: collision avoidance

Ping! Anyone still reviewing this patch?
I have another change related to AMS.
I will group them as a set and re-send it.

Regards,
Kyle Tso


On Mon, Apr 15, 2019 at 6:03 PM Adam Thomson
<Adam.Thomson.Opensource@...semi.com> wrote:
>
> On 13 April 2019 21:39, Hans de Goede wrote:
>
> > On 10-04-19 18:38, Hans de Goede wrote:
> > > On 10-04-19 18:14, Adam Thomson wrote:
> > >> On 10 April 2019 16:45, Hans de Goede wrote:
> >
> > <snip>
> >
> > >>> Starting toggling from tcpm_set_cc() just feels wrong; and currently
> > >>> power role swapping is broken with the fusb302, which IIRC used to
> > >>> work. I suspect this is related.
> > >>>
> > >>> I plan to write a patch tomorrow to functionally take tcpm_set_cc()
> > >>> back to the way it was before. This should fix your case and I hope
> > >>> this also fixes power-role swapping.
> > >>>
> > >>> This will re-introduce Adam Thomson's problem, but I have a feeling
> > >>> that that actually needs a fix in the tcpm.c code rather then at the fusb302
> > level.
> > >>
> > >> To be clear here, the names TOGGLING_MODE_SNK and
> > TOGGLING_MODE_SRC
> > >> are a misnomer from the HW spec for fusb302. The device isn't
> > >> toggling anything as far as I'm aware, so I don't necessarily agree with your
> > point.
> > >
> > > If I understand the datasheet correctly:
> > >
> > > "The FUSB302 has the capability to do autonomous DRP toggle. In
> > > autonomous toggle the FUSB302 internally controls the PDWN1, PDWN2,
> > > PU_EN1 and PU_EN2, MEAS_CC1 and MEAS_CC2 and implements a fixed DRP
> > > toggle between presenting as a SRC and presenting as a SNK.
> > > Alternately, it can present as a SRC or SNK only and poll CC1 and CC2
> > > continuously."
> > >
> > > It is still attaching Rp resp Rd to CC1 or CC2 one at a time to detect
> > > polarity, so it is still toggling, it just is not doing dual-role
> > > toggling. This is also expected behavior for a sink, a sink may not
> > > present Rd on both CC pins at the same time, otherwise the source
> > > cannot detect the polarity and the source also cannot detect if Vconn
> > > is necessary.
> > >
> > >> It's a mechanism to
> > >> have the HW report when the CC line changes on connection. Without
> > >> that we have no reporting from the HW for the fixed role scenarios.
> > >
> > > Not just connection, also polarity detection. Notice that the tcpm
> > > framework / the driver also has a start_drp_toggling() method. I think
> > > we may also need a start_srp_toggling function just like it and call
> > > that from the SNK_UNATTACHED and SRC_UNATTACHED states for single-role
> > > ports. I agree that we need to start toggling when in those states,
> > > but tcpm_set_cc gets called in a lot of other places where AFAIK we
> > > should NOT restart toggling and your patch causes us to restart
> > > toggling in those cases.
> >
> > Ok, so as I suspected, commit ea3b4d5523bc ("usb: typec: fusb302:
> > Resolve fixed power role contract setup") is what caused the power-role
> > swapping breakage I've been seeing.
>
> Apologies for the breakage. Annoyed I didn't catch that when submitting that
> patch. Thanks for looking to resolve this and will review your updates shortly.
>
> > So I've prepared a 3 patch series:
> >
> > 1) Add a new start_srp_connection_detect function which, when implemented
> > by the tcpc_dev, gets called instead of start_drp_toggling for single role ports
> > (SRPs)
> >
> > 2) Implement 1. for fusb302 to fix the SRP issue Adam was seeing, without
> > depending on set_cc starting "toggling"
> > or something like it for the fix
> >
> > 3) Revert commit ea3b4d5523bc, restoring power-role swap functionality.
> >
> > This should also fix the issue Kyle Tso was seeing when trying to change from one
> > Rp setting to another.
> >
> > I'll send out the series right after this email.
> >
> > Regards,
> >
> > Hans
>