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From:   Kyle Tso <kyletso@google.com>
Date:   Mon, 17 Dec 2018 21:17:37 +0800
Message-ID: <CAGZ6i=10sbGB9FpRauQ9Byx_jTUrNsrTbkydXmP-XG1Qrqo4sg@mail.gmail.com>
Subject: Re: [PATCH] usb: typec: tcpm: Extend the matching rules on PPS APDO selection
To:     Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Cc:     "linux@roeck-us.net" <linux@roeck-us.net>,
        "heikki.krogerus@linux.intel.com" <heikki.krogerus@linux.intel.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "badhri@google.com" <badhri@google.com>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Mon, Dec 17, 2018 at 8:45 PM Kyle Tso <kyletso@google.com> wrote:
>
> On Mon, Dec 17, 2018 at 8:23 PM Adam Thomson
> <Adam.Thomson.Opensource@diasemi.com> wrote:
> >
> > On 17 December 2018 02:48, Kyle Tso wrote:
> >
> > > Current matching rules ensure that the voltage range of selected Source
> > > Capability is entirely within the range defined in one of the Sink Capabilities. This
> > > is reasonable but not practical because Sink may not support wide range of
> > > voltage when sinking power while Source could advertise its capabilities in
> > > raletively wider range. For example, a Source PDO advertising 3.3V-11V@3A (9V
> >
> > relatively
> >
>
> noted!
> Thanks for the correction. I will fix this in the next patch.
>
> > > Prog of Fixed Nominal Voltage) will not be selected if the Sink requires 5V-
> > > 12V@3A PPS power. However, the Sink could work well if the requested voltage
> > > range in RDOs is 5V-11V@3A.
> > >
> > > Currently accepted:
> > >               |--------- source -----|
> > >       |----------- sink ---------------|
> > >
> > > Currently not accepted:
> > >                       |--------- source -----|
> > >       |----------- sink ---------------|
> > >
> > >       |--------- source -----|
> > >               |----------- sink ---------------|
> > >
> > >       |--------- source -----------------|
> > >               |------ sink -------|
> > >
> > > To improve the usability, change the matching rules to what listed
> > > below:
> > > a. The Source PDO is selectable if any portion of the voltage range
> > >    overlaps one of the Sink PDO's voltage range.
> > > b. The maximum operational voltage will be the lower one between the
> > >    selected Source PDO and the matching Sink PDO.
> > > c. The maximum power will be the maximum operational voltage times the
> > >    maximum current defined in the selected Source PDO d. Select the Source PDO
> > > with the highest maximum power
> > >
> > > Signed-off-by: Kyle Tso <kyletso@google.com>
> > >
> > > ---
> > > Changelog since v1:
> > > - updated the commit message as suggested by Guenter Roeck <linux@roeck-
> > > us.net>
> > > ---
> > >  drivers/usb/typec/tcpm/tcpm.c | 29 +++++++++++++++++------------
> > >  1 file changed, 17 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> > > index 3620efee2688..3001df7bd602 100644
> > > --- a/drivers/usb/typec/tcpm/tcpm.c
> > > +++ b/drivers/usb/typec/tcpm/tcpm.c
> > > @@ -2213,7 +2213,8 @@ static unsigned int tcpm_pd_select_pps_apdo(struct
> > > tcpm_port *port)
> > >       unsigned int i, j, max_mw = 0, max_mv = 0;
> > >       unsigned int min_src_mv, max_src_mv, src_ma, src_mw;
> > >       unsigned int min_snk_mv, max_snk_mv;
> > > -     u32 pdo;
> > > +     unsigned int max_op_mv;
> > > +     u32 pdo, src, snk;
> > >       unsigned int src_pdo = 0, snk_pdo = 0;
> > >
> > >       /*
> > > @@ -2263,16 +2264,18 @@ static unsigned int tcpm_pd_select_pps_apdo(struct
> > > tcpm_port *port)
> > >                                       continue;
> > >                               }
> > >
> > > -                             if (max_src_mv <= max_snk_mv &&
> > > -                                 min_src_mv >= min_snk_mv) {
> > > +                             if (min_src_mv <= max_snk_mv &&
> > > +                                 max_src_mv >= min_snk_mv) {
> > > +                                     max_op_mv = min(max_src_mv,
> > > max_snk_mv);
> > > +                                     src_mw = (max_op_mv * src_ma) / 1000;
> > >                                       /* Prefer higher voltages if available */
> > >                                       if ((src_mw == max_mw &&
> > > -                                          min_src_mv > max_mv) ||
> > > +                                          max_op_mv > max_mv) ||
> > >                                           src_mw > max_mw) {
> >
> > Sorry I didn't raise this before, but came to mind this morning when I was
> > considering your updates again. What happens if the Source validly provides two
> > PPS APDOs, for example:
> >
> >         3.3V - 11V, 3A (9V programmable)
> >         3.3V - 16V, 3A (15V programmable)
> >
> > and the sink APDO is:
> >
> >         5V - 9V, 3A
> >
> > I think the code here will now select the higher range (15V programmable) as it
> > gives a larger power output value, even if the sink can only support a voltage
> > that's far smaller. I really don't think this is correct. *If* you are going to
> > allow selection of PPS APDOs that provide a larger voltage range than the Sink
> > can actually cope with, then I think you should at least select the lower of
> > those advertised which fulfils the needs of the Sink.
>
> Source:
> 3.3V - 11V, 3A (9V programmable)
> 3.3V - 16V, 3A (15V programmable)
>
> Sink
> 5V - 9V, 3A
>
> In this case, the Sink will select "3.3V - 11V, 3A (9V programmable)"
> because the
> "max_op_mv" when dealing with both Source Cap will be the same.
>
> See line#2269, "max_op_mv" will be limited by "max_snk_mv" which is 9V.
> And in line#2273, "max_op_mv" (of the second src_cap) fails the check
> because "max_mv", which is equal to the "max_op_mv" of the previous src_cap,
> is the same as it.
>

Sorry, I should have explained more clearer here.
"max_op_mv" and "src_mw" are both limited to "max_snk_mv" (9V) in this
case. Therefore in the following "if" statement (line#2272 to line#2274), both
"src_mw" and "max_op_mv" remain the same as those regarding to
the previous src_cap. So the "if" statement will be "false".
==> select the previous src_cap

> 2267                             if (min_src_mv <= max_snk_mv &&
> 2268                                 max_src_mv >= min_snk_mv) {
> 2269                                     max_op_mv = min(max_src_mv,
> max_snk_mv);
> 2270                                     src_mw = (max_op_mv * src_ma) / 1000;
> 2271                                     /* Prefer higher voltages if
> available */
> 2272                                     if ((src_mw == max_mw &&
> 2273                                          max_op_mv > max_mv) ||
> 2274                                         src_mw > max_mw) {
> 2275                                             src_pdo = i;
> 2276                                             snk_pdo = j;
> 2277                                             max_mw = src_mw;
> 2278                                             max_mv = max_op_mv;
> 2279                                     }
> 2280                             }
>
> >
> > >                                               src_pdo = i;
> > >                                               snk_pdo = j;
> > >                                               max_mw = src_mw;
> > > -                                             max_mv = max_src_mv;
> > > +                                             max_mv = max_op_mv;
> > >                                       }
> > >                               }
> > >                       }
> > > @@ -2285,14 +2288,16 @@ static unsigned int tcpm_pd_select_pps_apdo(struct
> > > tcpm_port *port)
> > >       }
> > >
> > >       if (src_pdo) {
> > > -             pdo = port->source_caps[src_pdo];
> > > -
> > > -             port->pps_data.min_volt = pdo_pps_apdo_min_voltage(pdo);
> > > -             port->pps_data.max_volt = pdo_pps_apdo_max_voltage(pdo);
> > > -             port->pps_data.max_curr =
> > > -                     min_pps_apdo_current(pdo, port->snk_pdo[snk_pdo]);
> > > +             src = port->source_caps[src_pdo];
> > > +             snk = port->snk_pdo[snk_pdo];
> > > +
> > > +             port->pps_data.min_volt =
> > > max(pdo_pps_apdo_min_voltage(src),
> > > +                                           pdo_pps_apdo_min_voltage(snk));
> > > +             port->pps_data.max_volt =
> > > min(pdo_pps_apdo_max_voltage(src),
> > > +                                           pdo_pps_apdo_max_voltage(snk));
> > > +             port->pps_data.max_curr = min_pps_apdo_current(src, snk);
> > >               port->pps_data.out_volt =
> > > -                     min(pdo_pps_apdo_max_voltage(pdo), port-
> > > >pps_data.out_volt);
> > > +                     min(port->pps_data.max_volt, port-
> > > >pps_data.out_volt);
> > >               port->pps_data.op_curr =
> > >                       min(port->pps_data.max_curr, port->pps_data.op_curr);
> > >       }
> > > --
> > > 2.20.0.405.gbc1bbc6f85-goog
> >