linux-kernel - Re: [PATCH] usb: typec: tcpm: Create legacy PDOs for PD2 connection

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Message-ID: <CAGZ6i=0M6=cZpfm=Eu4s4XTjwz5GPbpStNNOdjnPAkJ1y2MRRA@mail.gmail.com>
Date:   Thu, 21 Jan 2021 17:48:46 +0800
From:   Kyle Tso <kyletso@...gle.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Greg KH <gregkh@...uxfoundation.org>,
        Badhri Jagan Sridharan <badhri@...gle.com>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: typec: tcpm: Create legacy PDOs for PD2 connection

On Thu, Jan 21, 2021 at 4:41 PM Heikki Krogerus
<heikki.krogerus@...ux.intel.com> wrote:
>
> Hi Kyle,
>
> On Sat, Jan 16, 2021 at 12:33:11AM +0800, Kyle Tso wrote:
> > If the port partner is PD2, the PDOs of the local port should follow the
> > format defined in PD2 Spec. Dynamically modify the pre-defined PD3 PDOs
> > and transform them into PD2 format before sending them to the PD2 port
> > partner.
>
> I guess it's not possible for the system to supply separate static
> PDOs for each PD revision?
>
We can do that for sure. But a problem is that if there are more PD
revisions in the future, we will need to add more PDO arrays.
For backward compatibility, the new revision usually uses the
previously-reserved bits for the new features.
>From my perspective, the better way to achieve the backward
compatibility is to just clear the bits if those are reserved in the
previous revision.

I can submit another patch which adds another PDO array for PD2 if you
think it is more appropriate.

> > Signed-off-by: Kyle Tso <kyletso@...gle.com>
> > ---
> >  drivers/usb/typec/tcpm/tcpm.c | 62 +++++++++++++++++++++++++++++------
> >  include/linux/usb/pd.h        |  1 +
> >  2 files changed, 53 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> > index 22a85b396f69..1220ab1ed47d 100644
> > --- a/drivers/usb/typec/tcpm/tcpm.c
> > +++ b/drivers/usb/typec/tcpm/tcpm.c
> > @@ -911,13 +911,47 @@ static int tcpm_set_pwr_role(struct tcpm_port *port, enum typec_role role)
> >       return 0;
> >  }
> >
> > +/*
> > + * Transform the PDO to be compliant to PD rev2.0.
> > + * Return 0 if the PDO type is not defined in PD rev2.0.
> > + * Otherwise, return the converted PDO.
> > + */
> > +static u32 tcpm_forge_legacy_pdo(struct tcpm_port *port, u32 pdo, enum typec_role role)
> > +{
> > +     switch (pdo_type(pdo)) {
> > +     case PDO_TYPE_FIXED:
> > +             if (role == TYPEC_SINK)
> > +                     return pdo & ~PDO_FIXED_FRS_CURR_MASK;
> > +             else
> > +                     return pdo & ~PDO_FIXED_UNCHUNK_EXT;
> > +     case PDO_TYPE_VAR:
> > +     case PDO_TYPE_BATT:
> > +             return pdo;
> > +     case PDO_TYPE_APDO:
> > +     default:
> > +             return 0;
> > +     }
> > +}
> > +
> >  static int tcpm_pd_send_source_caps(struct tcpm_port *port)
> >  {
> >       struct pd_message msg;
> > -     int i;
> > +     u32 pdo;
> > +     unsigned int i, nr_pdo = 0;
>
> Side note. I think this driver uses the "reverse christmas tree"
> style with the variables.

I will change the order (if there is a next version)

thanks,
Kyle