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

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Message-ID: <AM5PR1001MB099452876C75E45FD774BA77802B0@AM5PR1001MB0994.EURPRD10.PROD.OUTLOOK.COM>
Date:   Mon, 15 Apr 2019 10:03:13 +0000
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        Kyle Tso <kyletso@...gle.com>
CC:     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

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